问题补充：
—Hi，Joan.Any idea where Tom is?
—He on the playground.I saw him there playing football just now.
A. shall be
B. should have been
C. must be
D. might have been
答案：
A. shall be
B. should have been
C. must be
D. might have been
解析：句意：——嗨，Joan。你知道Tom在哪里吗？——一定在操场上，我刚才看见他在操场上踢足球。must be是对现在状态的肯定推测。 答案C
