下面这段话应选择的最恰当的一组关联词是________任何生物的活动都有时间上的周期性节奏，________宇宙飞船中宇航员的活动也要符合地球上昼夜循环的规律，白天工作，夜间休息，________他们在密闭舱里，没有习以为常的昼夜交替，________通过仪表和控制台使之同地球上生活的人的睡眠一致，________睡眠不好，他们会感到筋疲力尽，________无法完成宇航任务。

It was not until dark ________ he found ________ he thought was the correct way to solve the problem.

How long have you ____here—For two days. I _____here the day before yesterday.

Korean star PSY’s “Gangnam style” video,________,has set the Guinness World Record for the most “liked” video in YouTubehistory

y, it’s already 6 o’clock. I have to beoff for an appointment. — OK. ________. See you.