3. ________conclusion, I think that cars are very useful because travel is so easy with a car.

2.Mary got into an argument____her sister over the housework.

B.根据句意使用恰当的词填空（注意：填入的单词数量不得多于3个）

1.―Do you know why the river was polluted?

―Many different factors contributed____the serious pollution of the river.

10. If the mixture is too hard, you will need to____ ____ (soft) it.

9.There's no________ (just) in the world when people can be made to suffer like that.

8.We searched all the morning for the missing papers and finally________ (discover) them in a drawer.

7.Someone thought that it might be the first time the two officials ____ (be) together in a place where they could get to know each other.

6.I'm sure your suggestions will contribute to ____  (solve) the problem.

5.The invention of paper was a great____ (contribute) to human civilization.

4.Don't you know Alexander Graham Bell is the________ (invent) of the telephone?