Don’t let the child who is go to school．
A. so young as to
B. not old enough to
C. not old enough
D. too young to
网友回答
A. so young as to
B. not old enough to
(答案→)C. not old enough
D. too young to
解析：这题考查定语从句：who is old enough是定语从句，修饰the child，而谓语let后面接宾语+省略to的不定式。选C。句意是：别让年龄不够的孩子上学。