问题
选择题
---Has Tom finished his job yet?
---I have no idea of it; he _____ it this morning.
A．has been doing
B．had been doing
C．did
D．was doing
答案
答案：D
考查时态。表示过去某一时刻正在进行的动作用过去进行时态。句意：汤姆完成他的工作了吗？我不清楚，他整个上午一直在做。所以选D。
，则f[g(x)]=______。