问题补充：
Being constantly exposed to advertisements is annoying, but it be pleasant sometimes.
A. shall
B. need
C. can
D. must
答案：
A. shall
B. need
(答案→)C. can
D. must
解析：考查情态动词：句意：经常看到广告让人恼火，但有时也是令人愉快的。A. shall表示“命令，警告，允诺，征求意见”， B. need需要，C. can能，有可能，会，D. must必须，这里用can表示“有客观可能性”，选C。
