问题补充:
So fast that I could not catch up with them.
A. did they run
B. they had run
C. they ran
D. had they run
答案:
(答案→)A. did they run
B. they had run
C. they ran
D. had they run
解析:考查倒装句:在so... that…结构中,若将so+adj. / adv. 置于句首,则其后的主句要用部分倒装。句意:他们跑得如此快,以至于我不能赶上他们。由句意可知是过去时,提前did,选A。