So it would have been nice to have this at a later hour but this was the only time that really worked into the schedule, so I appreciate you being here.
所以,如果能晚一点上课当然好,但这是课程表唯一能排出来的时间,所以我很高兴你们能来上课
They had to give some of them the real vaccine and some of them a placebo vaccine in order that they could really tell if the vaccine worked; you have to have it placebo controlled.
研究者们还须给部分孩子接种真正的疫苗,给另外一些孩子接种空白疫苗,以分辨疫苗是否真的有效,所以你必须使用安慰剂作对照
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