求助两道GWD语法题~~~~

emircufe

GWD-29-Q40
Most of Portugal’s 250,000 university students boycotted classes in a one-day strike to protest a law that requires them to contribute $330 a year toward the cost of higher education, previously paying $7 per year.
A.year toward the cost of higher education,  previously paying $7 per year
B.year toward the cost of higher education,  for which was previously paid $7 per year
C.year,  compared to the previously $7 per year, toward the cost of higher education
D.year toward the cost of higher education, instead of the $7 per year required previously
E.year as opposed to the $7 per year required previously for the cost of higher education
讲解说A-paying的逻辑主语是a law，为什么不是主句主语啊？
GWD28-Q21
According to entomologists, single locusts are quiet creatures, but when locusts are placed with others of their species, they become excited, change color, vibrate, and even hum.
A.when locusts are placed with others of their species,
B.when placing them with others of their species, then    placing的逻辑主语是they（locusts），错
C.locusts, when placed with others of their species,
D.placing them with others of their species,
E.placed with others of their species, then
求助E为什么不对？

谢谢各位牛人了！！

eshopaholic

GWD-29-Q40
Most of Portugal’s 250,000 university students boycotted classes in a one-day strike to protest a law that requires them to contribute $330 a year toward the cost of higher education, previously paying $7 per year.

A 从结构上看，previously paying .... 从属于定语从句a law that requires.... 所以逻辑主语不对。

emircufe

谢谢 但是怎么看从属于定语从句，什么时候就是主句主语啊？我每次做题遇到这类问题，都有些不太明白

lovereve

第二题，E选项中placed修饰谁啊？无法确定，是locusts还是creatures

paopaogjp

B.year toward the cost of higher education,  for which was previously paid $7 per year
哪里不对呢？就是学费之前是每年7刀的。