Students must be strict their studies and teachers should be strict their students.A. in

问题补充：

Students must be strict their studies and teachers should be strict their students.

A. in, at

B. at, with

C. with , in

D. in, with

答案：

A. in, at

B. at, with

C. with , in

(答案→)D. in, with

解析：根据语境可知此句的含义是学生必须要严格要求他们的学习，老师们也应该严格要求他们的学生。其中涉及到固定短语be strict in sth和be strict with sb的基本用法，前者表示对某事要求严格，后者表示对某人要求严格。根据选择项的提示可知选择D。