问题补充：
The students asked .
A. when can they surf the Internet in class
B. when could they surf the Internet in class
C. when they could surf the Internet in class
D. when they can surf the Internet in class
答案：
A. when can they surf the Internet in class
B. when could they surf the Internet in class
(答案→)C. when they could surf the Internet in class
D. when they can surf the Internet in class
解析：考查时态和宾语从句的语序。所有的名词性从句都使用陈述语序，排除AB；asked是过去时，后面的宾语从句也应该使用过去时。
