填空题 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


  • 1、
【正确答案】 1、B应改为falling asleep。    
【答案解析】[解析] have trouble doing sth.