either of和neither of在否定句中的区别

I don't want____the books,thank you.(A)
A.either of B.both of
He could not answer____the questions I asked.(A)
A.neither of B.either of

I don't want____the books,thank you.(A)
A.either of B.both of
选项A。 意思是：“我不想要这两本书的任何一本”。即：这两本书我都不要。
He could not answer____the questions I asked.(A)
A.neither of B.either of
选项A。 句子是双重否定。意思是：“我问的两个问题，没有一个他回答不了的”。即：“我问的两个问题，他都能回答”。