A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior. If 2 students to be selected at random form each class, what is the probability that the 2 students selected will be a sibling pair? A) 3/40000 B) 1/3600 C) 9/2000 D) 1/60 E) 1/15
Maybe i think it too complicated, anyway i can't calculate an answer here.
At least 100 students at a certain high school study Japanese. If 4% of the students at the school who study French also study Japanese, do more students at school study French than Japanese? 1) 16 students at the school study both French and Japanese 2) 10% of the students at the school who study Japanese also study French
I chose both 1) and 2), can't understand who 1) can't fullfil here... i think the meaning shall be the same as 2)
语法：
Concerns about public health led to the construction between 1876 and 1904 of three seperate sewer systems to serve metropolotan Boston.
B) Concerns about public health have led to the construction of three seperate sewer system between 1876 and 1904 to serve...
here i can't understand why "led" instead of "have led" is used here... why "have led" is not acceptable?
Appreciate NN's reply and advice. Thanks alot!!!作者: tracyforever 时间: 2010-3-28 14:03
自己顶起来！作者: sissizhx 时间: 2010-3-29 15:03
现在完成时 表示动作发生在过去，但与现在的情况有联系 表示从过去某一时间开始一直延续到现在并还可能继续延续下去的动作，在此 between 1876 and 1904清楚地说明动作已经结束~~所以用过去式。
