The population in this country is 5 times ______ that in the
2个回答

1.你是对的,这题是选B.答案错了.如果选D的话,large前面还要有一个as.即 ...5 times as large as .

2.with whom your mother is talking是定语从句,如果把它还原成一个独立的句子,就是:

Your mother is talking with her.(你妈妈正在跟她谈话.)

从这里可以看出,介词with在这里是不可少的.

定语从句的详细用法是高一学的,这里就不说了.