求助GWD上的两道语法题，谢谢o(∩_∩)o

Helloface

都是排除了三个，二选一我选错了但是不知道为什么错的。
1. In his experiments with gravity, Isaac Newton showed how the motion of each planet in the solar system results from the combined gravitational pull of the Sun and of all the other planets, each contributing according to their mass and distance from the others. B对
A.    all the other planets, each of which contributing according to its   which引导的是定语从句，没有谓语
B.    all the other planets, each contributing according to its
如果要A对，那应该怎么改呢？？

2. 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.B对
A.    year toward the cost of higher education, for which was previously paid $7 per year  pay的主语是谁不明确
B.    year toward the cost of higher education, instead of the $7 per year required previously
which不是指代education么，那education was paid for $7怎么会没有主语啊……？

求解答~~~~~~~

Helloface

好详细~~明白啦~~~谢谢

一丝不挂

1、如果A要对的话，可以改成all the other planets, each of which contributes according to its
2、A选项里面的which可以指代education但是也可以指the cost of higher education，因为原则上high education是来修饰cost的，cost才是核心词。如果说education was paid 是没问题的，但是说the cost of higher education was paid就是语义重复，不简洁了。

Helloface

呜呜呜呜呜，木有人理我T.T