题目内容：

It is not until ______ that ______.

A. is a baby kangaroo four months old; he will begin to live outside its mother’s pouch

B. is a baby kangaroo four months old; will he begin to live outside its mother’s pouch

C. a baby kangaroo is four months old; he will begin to live outside its mother’s pouch

D. a baby kangaroo is four months old; will he begin to live outside its mother’s pouch