问题
选择题
The children ＿＿very quiet；I wonder what they ＿＿up to.
A．were； are being
B．are being；are
C．are；do
D．are being；do
答案
答案：B
be用于进行时可表示一个暂时的特点或表现。What they are up to相当于What they are doing。
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