Obviously, he’s very disappointed at the way things have ____. A. turned up B. turned out C. turned on D. turned down 答案:B根据下面的提示,给太空行走下一个明确的定义。①太空行走是一种通俗的叫法,科学术语应该是“出舱活动”。②太空行走时航天员必须穿着出舱活动航天服。③太空行走时宇航员将离开飞船、航天飞机或空间站。④太空行走中宇航员将进入宇宙空间完成指派的各种任务。④太空行走包括在月面上或是在火星上行动的过程。答: