You phone him if you want to, but you ! He will surely phone you.
A. may; mustn’t
B. have to; needn’t
C. can; needn’t
D. can; doesn’t need
网友回答
A. may; mustn’t
B. have to; needn’t
(答案→)C. can; needn’t
D. can; doesn’t need
解析：表示“你可以”用you may或you can都正确，B项肯定不对，关键还是need的用法，根据下文He will surely phone you soon，可知“你没必要”，因此排除A，mustn’t“不许；禁止”，语气不对，D错在主谓搭配不一致。