用the number of 或 a number of 填空
问题描述：
用the number of 或 a number of 填空
1.（ ）cares on the roads has doubled over the past few years in our country.
2.We have been friends for ( )years.
理由要说
答
1.the number of
车的数量增加了
2.a number of
我们做朋友已经很久了