最近复习语法，弱智问题挺多 求好心人指导

carlosh

第一问：
New hardy varieties of rice show promise of producing high yields without the costly irrigation and application of commercial fertilizer that were required by earlier high-yielding varieties.
我写的是正确答案，我想问的是irrigation of fertilizer 是什么意思？ 这会造成意思上的逻辑错误么？

第二问：

While some academicians believe that business ethics should be intergraed into every business course, others say that student will take ethics seriously only if it is taught as a separate, required course.
这是正确答案，想问的是逗号连接词语时候的用法，这里separate和required之间逗号的作用和and一样么？ 是不是连接词语的时候and和逗号可以互换呢，还是只有连个词语的时候是这样呢？
第三问：
Certain pesticides can become ineffective if used repeatedly in the same place:one reason is suggested by the finding that there are much larger populations of pesticide-regarding microbes in soils with a relatively long history of pesticide use than in soils that  are free of such chemicals.
这句也是正确答案，请问句中的冒号是什么意思，我觉得可以用分号，为什么这里用的冒号？
第四问：
A huge flying reptile that died out with the dinosaurs some 65 million years ago, the Quetzal-caotlus had a wingspan of 36 feet, and it is believed to have been the largest flying creature the world has ever seen.
给的是正确答案，请问it为什么指代主语reptile，不能指代wingspan么？ 我做题的时候觉得这里有歧义，请问it指代的用法，这个问题比较麻烦，但是恳请好心人帮忙~~~

能回答一个也行，不用全回答，先谢谢大家

carlosh

亲爱的CD战友们，请帮帮在苦海中挣扎的我 谢谢

bababa11111

第一问 irrigation

parallel to

application of commercial fertilizer

carlosh

谢谢上面的回答，可是为什么irrigation不能修饰fertilizer呢，A and B of C，也可以AB同时修饰C 吧？是不是因为后面的动词用的是were？ 只能是A and BofC？

lxw19

感觉从句意上就说不通吧 如果irrigation and application 同时修饰 commercial fertilizer的话 那翻译过来不就成了“化肥的灌溉与应用 ”  可是灌溉是用水进行灌溉 所以逻辑上不通啊

carlosh

所以我觉得这个修饰有问题，语法上应该irrigation应该是可以修饰commercial fertilizer的啊 但是逻辑意思上就不对了，这不是应该叫产生歧义 是错误的么？