几道关于初三英语主谓一致的问题，求大神讲解。

几道关于初三英语主谓一致的问题，求大神讲解。
14. Although the first part of the book is easy， the rest _B_____.
A. aredifficult

B. has proved difficult

C. is supposeddifficult

D. have been found difficult
为什么选B句子是什么意思
Thatthey were wrong in these matters _A____ now clear to us all.
A. is B. was C.are D. were
16. Half of his goods __B__ stolen theother day.
A. are B. were C.is D. was
half of做主语，不是应该和后名词保持一致么？，后面没有名词啊？
17. Mathematics _C___the language of science.
A. are B. aregoing to be C.is D.is to be
Mathematics是指无生命集合体么？D是什么意思
18. Each of the students __B___ a Chinese-English dictionary.
A. have B.has C. there is D. there are
each这里只是表示修饰,主语还是they 所以复数
那为什么each表修是啊？？
求讲解，详细点，有点多，三克油，，，