Among the 15-year-old children some studying in university while others are still learnin

问题补充：

Among the 15-year-old children, some studying in university while others are still learning to read and write.

A. should have been

B. would have been

C. can be

D. must be

答案：

A. should have been

B. would have been

(答案→)C. can be

D. must be

解析：考查情态动词。句意：在十五岁的孩子中间，一些可能在大学学习，然而另一些仍旧在学习读写。选项AB为虚拟语气，选项D为肯定推断，结合语境可知选C。