护卫舰的任务是什么？
参考答案：
它的主要任务是巡逻、警戒和护卫海上战斗舰艇、运输船队，防止敌人潜艇、鱼雷艇和航空兵的袭击。
---_________ ?
---I’m not sure, but he might have been ill in bed.
A．What do you think has happened to Tom
B．What do you think Tom has happened
C．Do you think what has happened to Tom
D．Do you think what Tom has happened
大洋中脊
