问题补充：
－I think students should be allowed homework with friends.
－I disagree. They talk instead of homework.
A. do, doing
B. to do, to do
C. to do, doing
D. doing, to do
答案：
A. do, doing
B. to do, to do
(答案→)C. to do, doing
D. doing, to do
解析：be allowed to do sth，表示被允许做某事，而instead of 为介词后街动词现在分词形式，故选C
