阅读下面短文，掌握其大意，从题中所给的A、B、C三个选项中选出一个最佳答案填空。
A boy was walking in the street 1 a man came over 2 him and 3 him the way4 the station.
The boy was very naughty（顽皮的）. He wanted 5 play a joke on the man. He pointed to6side of the road and said, “Go down the street until you reach a shop. You can find it on your left.” The man thanked him and went away.
A few minutes 7, the man came back. He said to boy that there was only a bookshop there and he 8 find the station.
The boy 9 and said, “10a map in the bookshop, and you'll find the way!”
,定义函数
,若
两两不相等，且
为不小于6的偶数，则满足上述条件的不同的函数
有（ ）个
