问题
选择题
When the old man _______ to walk back to his house, the sun ________ itself behind the mountain.
A．started; had already hidden
B．had started; had already hidden
C．had started; was hiding
D．was starting; hid
答案
答案：A
老人开始跑回家与太阳落山两个动作都发生在过去，而后者又发生在前者之前，故前者用一般过去时，后者用过去完成时。