og 237,238 a number of主谓一致

237. It seems likely that a number of astronomical phenomena, such as the formation of planetary nebulas, may
be caused by the interaction where two stars orbit each other at close range.
(A) may be caused by the interaction where two stars orbit each other
(B) may be caused by the interaction between two stars that each orbit the other
(C) are because of the interaction between two stars that orbit each other
(D) are caused by the interaction of two stars where each is orbiting the other
(E) are caused by the interaction of two stars orbiting each other

正确答案是E

238. According to a recent study by Rutgers University, the number of women in state legislatures has grown in
every election since 1968.
(A) the number of women in state legislatures has grown
(B) the number of women who are in state legislatures have grown
(C) there has been growth in the number of women in state legislatures
(D) a growing number of women have been in state legislatures
(E) women have been growing in number in state legislatures

答案是A

我的疑问是：a number of +名词复数＋谓语动词单数，为什么这个原则在237中不适用？

还有是否是我记混了，a number of和the number of是有区别的，谁能给个确定意见，谢谢。

a number of +名词复数＋谓语动词复数，a number of 是许多的意思。

the number of +名词复数＋谓语动词单数,中心词是the number，指...的数目。