问题1：if x do, y will do 和 if x do, y do 意思上有什么区别？
问题2： if从句 在主句前和主句后有分别什么特殊要求吗？比如：y will do if x do 或者 if x do, y will do
问题3：用在主句前， 主从句之间要加逗号，那用在主句后加不加逗号有规定吗？
以下是2道不同时态的例子
46. A study commissioned by the Department of Agriculture showed that if calves exercise and associated with other calves, they will require less medication and gain weight quicker than do those raised in confinement.
(A) associated with other calves, they will require less medication and gain weight quicker than do
(B) associated with other calves, they require less medication and gain weight quicker than
(C) associate with other calves, they required less medication and will gain weight quicker than do
(D) associate with other calves, they have required less medication and will gain weight more quickly than do（E）
(E) associate with other calves, they require less medication and gain weight more quickly than
The first verb in the clauses introduced by showed that is exercise. A and B incorrectly compound that present tense verb with a past tense verb, associated. C and D correctly use associate, but C follows with the past tense required and D with the present perfect have required. Both C and D incorrectly conclude with the future tense will gain.
（这里用will gain 错误的原因应该是和require不平行， 但如果前面是will require, 那这里用will gain应该没问题吧？）
37. While some academicians believe that business ethics should be integrated into every business course, others say that students will take ethics seriously only if it would be taught as a separately required course.
(A) only if it would be taught as a separately required course
(B) only if it is taught as a separate, required course
(C) if it is taught only as a course required separately
(D) if it was taught only as a separate and required course（B）
(E) if it would only be taught as a required course, separately
Choice B is best: in sentences expressing a conditional result (x will happen if y happens),
...
x will happen if y happens里的2个时态是idiom还是根据逻辑意思决定呢？
个人认为，第一道题目，CD在平行上完全不能对应，而平行是GMAT经常考到的错误，所以，从这个角度来讲，E更好些。
谢谢楼上两位
可能我说的不够清楚
46. A study commissioned by the Department of Agriculture showed that if calves exercise and associated with other calves, they will require less medication and gain weight quicker than do those raised in confinement.
(A) associated with other calves, they will require less medication and gain weight quicker than do
(B) associated with other calves, they require less medication and gain weight quicker than
(C) associate with other calves, they required less medication and will gain weight quicker than do
(D) associate with other calves, they have required less medication and will gain weight more quickly than do（E）
(E) associate with other calves, they require less medication and gain weight more quickly than
answer:E
显然，这里不用x will happen if y happens , 而是用了if y happens, x happens.
不用will gain的原因是要和require平行 没错， 但是为什么不直接用will require and will gain呢？就是说if y happens, y happens 也一样有效
我主要的问题是， 这两种表达在用法上有区别吗？有没有可能是“showed”这个过去时造成的， 因为后面的都是showed的内容。
showed的内容是一个规律性的客观的事实， 所以应该没有受showed的影响
x will happen if y happens
if y happens, x happens
没区别了？？
自己顶
正好在做总结 这种用法导致做这类题的时候不能简单通过“主将从现”来判断
请NNs指点
问题1：if x do, y will do 和 if x do, y do 意思上有什么区别？
问题2： if从句 在主句前和主句后有分别什么特殊要求吗？比如：y will do if x do 或者 if x do, y will do
问题3：用在主句前， 主从句之间要加逗号，那用在主句后加不加逗号有规定吗？
以下是2道不同时态的例子
46. A study commissioned by the Department of Agriculture showed that if calves exercise and associated with other calves, they will require less medication and gain weight quicker than do those raised in confinement.
(A) associated with other calves, they will require less medication and gain weight quicker than do
(B) associated with other calves, they require less medication and gain weight quicker than
(C) associate with other calves, they required less medication and will gain weight quicker than do
(D) associate with other calves, they have required less medication and will gain weight more quickly than do（E）
(E) associate with other calves, they require less medication and gain weight more quickly than
The first verb in the clauses introduced by showed that is exercise. A and B incorrectly compound that present tense verb with a past tense verb, associated. C and D correctly use associate, but C follows with the past tense required and D with the present perfect have required. Both C and D incorrectly conclude with the future tense will gain.
（这里用will gain 错误的原因应该是和require不平行， 但如果前面是will require, 那这里用will gain应该没问题吧？）
37. While some academicians believe that business ethics should be integrated into every business course, others say that students will take ethics seriously only if it would be taught as a separately required course.
(A) only if it would be taught as a separately required course
(B) only if it is taught as a separate, required course
(C) if it is taught only as a course required separately
(D) if it was taught only as a separate and required course（B）
(E) if it would only be taught as a required course, separately
Choice B is best: in sentences expressing a conditional result (x will happen if y happens),
...
x will happen if y happens里的2个时态是idiom还是根据逻辑意思决定呢？
第一题用一般现在时,表示的是一般情况.解释了study表现的内容.说明改情况已经发生,不存在给定条件A,B将要发生的意思
if x do, y will do 和 if x do, y do 意思上有区别,用在不用的情况,请仔细体会
转自新浪
if既可引导一个真实条件状语从句又可引导一个非真实条件状语从句，二者主要在以下三个方面有所不同：
一、 意义及谓语动词形式不同
如果该条件纯属假设，谓语动词用虚拟语气；有可能实现的条件则使用动词通常的陈述形式：
1.非真实条件状语从句的谓语动词用动词过去式来表示与现在事实相反或难以实现的愿望，主句则用“would+动词原形”；而真实条件状语从句的谓语动词用动词的一般现在时表示一般或未来情形下的条件，主句用一般现在时或将来时。试比较：
If my husband were a woman, he would understand my feelings a bit better. 如果我丈夫是个女人的话，他就会更好一点儿理解我的感情了。(丈夫不可能是女人)
Oil floats if you pour it on water. 如果你把油倒在水上，它就漂浮在上面。(能实现的事实)
2. 非真实条件状语从句的谓语动词用“had+过去分词”表示与过去的事实相反，主句用“would have done”；真实条件状语从句用一般过去时指过去的事实或用于间接引语中(可表示过去将来的情况)，主句用一般过去时或过去将来时。试比较：
If I had been a teacher at that time, I would have argued with him. 当时我要是老师的话，就和他争辩了。(事实上当时不是老师)
If Mike was a liar, it was for my sake. 如果麦克曾经是个撒谎的人，那也是为了我。(当时麦克极有可能是撒了谎)
He said he would go there if it was fine the next day. 他说，如果第二天天气好他就去那里。
二、 从句所接的情态动词的含义不同
1. if I (we, you, he...) +“ should + 动词原形”或“ were to +动词原形”或动词过去式，表示对将来情况的虚拟假设，即某事不会或不太可能发生，具有较大的试探性。如：
If you should run into Peter, please tell him he owes me a letter. 假如你碰见皮特，告诉他他该给我写信了。
What would you do if war were to break out? 如果战争爆发，你会怎么办？
2. if引导的真实条件状语从句一般很少使用将来时态，但有时也可用情态动词will或would来表示“愿望”(如果……愿意……)，甚至可用这种方式提出请求。如：
It'll make me very happy if you'll accept it. 如果你愿意收下它我会很高兴的。
If you will wait a moment, I'll go and tell the manager that you are here. 如果你愿意等一会儿，我就会去告诉经理你来了。
If you will hold my bag, I'll open the door (i.e. please hold my bag). 如果你愿意替我拿包，我就开门(即，请替我拿包)。
三、 与其他句型的转换不同
1.非真实条件状语从句中的if可省略，从句可以用倒装语序；而真实条件状语从句一般不可以。如：
If he were my son, I would beat him. 如果他是我的儿子我就打他。→Were he my son, I would beat him. (√)
If you touch me again, I'll call the police. 你再碰我，我就叫警察。→Do you touch me again, I'll call the police. (×)
2. 真实条件状语从句可以转换为“祈使句+and +陈述句”，而非真实条件状语从句则不可以。如：
If you touch me again, I'll call the police.→(You) Touch me again and I'll call the police. (√)
3. 真实条件状语从句的否定式可与unless ...转换，而非真实条件状语从句的否定式却不能。如：
If it doesn't rain tomorrow, I'll plant the flowers. 如果明天不下雨，我就把花栽上。→I'll plant the flowers unless it rains tomorrow. (√)
If it hadn't been for you, I would have failed in the exam. 如果不是你的话我就不会通过考试了。→Unless it had been for you, I would have failed in the exam. (×)
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