单项选择题
It is difficult ()a world record and even more difficult to () it.
A. keeping, set B. keep, set C. set, keep D. to set, keep
单项选择题 We should always () our opinion () facts.
单项选择题 The game will take place ()June 2nd.
单项选择题 So far there is no proof () spaceships from other planets do exist．
