单选题 It is extremely difficult or even impossible to {{U}}work out{{/U}} the risk of occasional passive smoking.
  • A. calculate
  • B. exercise
  • C. eliminate
  • D. convert
【正确答案】 A
【答案解析】work out：健身，解答，计算，解决；calculate：计算；exercise：锻炼，实施，练习，演习；eliminate：消灭，淘汰；convert：转化，转换，转变。