The stronger the _____is, the more quickly a man will learn a new skill. In other words, it is up to whether he has an interest in it.

 The two friends had a quarrel about money, but shortly afterwards they shook hands and _______.

(2013·浙江，4)As the world's population continues to grow，the ________ of food becomes more and more of a concern.

According to the American law, parents must keep their kids _______ except when they are in school.

 It has something to do with the part electricity ______ in our life.