Is Jack in the library—No, I saw him ___________ out with some books just now.

_______ , athletes from all over the world compete _______ the Olympic Games _______ the honor of winning.

下列各句中，划线的成语使用恰当的一句是 （ ）

______ the working efficiency,the boss allows the employees to have a coffee break. [ ]

Cloning humans has been _____ in the science world for many years and it is likely to continue .