单项选择题
Some scientists are checking the rocket a fifth time before it is launched. They must be very careful. You know, ______.
单项选择题 The morpheme "cast" in the common word "telecast" is a(n) ______.
单项选择题 —Patience is a good quality. —Yes, that is ______ it takes to do anything well.
单项选择题 They are good friends, ______ is no wonder that they know each other so well.
