英语,用词的适当形式填空.As research techniques become more advanced,the
英语,用词的适当形式填空.
As research techniques become more advanced,the number of animals
_______(use)in experiments may decrease.
我觉得应该是be used啊.答案是used.为什么?
如果是定语从句省略,那么到底是which is used 还是which are used