问题补充：
Jack is go to school,so his mother has to stay at home to look after him.
A. young enough to
B. old enough to
C. too young to
D. very old to
答案：
A. young enough to
B. old enough to
(答案→)C. too young to
D. very old to
解析：考查too…to…太……而不能结构。 根据so his mother has to stay at home to look after him可知他太小而不能去上学，所以选C。
