Is it the fact ____ he hasn’t turned in his research report?
(年北京市西城区高三5月二模试题)31. A person who has never tasted bitter won’t know ______ sweet is.
It suddenly occurred to him he had left his keys in the office.
(年北京市西城区高三5月二模试题)23. It’s been discovered in the study ______ people are more relieved after forgiving others.
The last time we had great fun was _____ we were visiting the Water Park.
(年安徽省合肥市高三第三次教学质量检测)31. What the whole nation cares about most at present is ______ the rescue teams could find the missing plane.