单选题 Some of these studies (have shown) that although some people have trouble (to fall asleep), others have an (equally) difficult time (waking up).
  • A. have shown
  • B. to fall asleep
  • C. equally
  • D. waking up


【正确答案】 B
【答案解析】改为falling asleep，have trouble/difficulty (in) doing sth．类似结构还有It's no use (useless/pointless) doing sth．。