--Don’t too late or you will feel sleepy in class.--I won’t Mum. Good night!A. put upB.

问题补充：

--Don’t too late, or you will feel sleepy in class.

--I won’t, Mum. Good night!

A. put up

B. cut up

C. end up

D. stay up

答案：

A. put up

B. cut up

C. end up

(答案→)D. stay up

解析：根据后文内容or you will feel sleepy in class.可知答案为D，表示不要熬夜太迟，故选D