A

    A king loved music. One day, a man 1 the king a harp (竖琴). When the king played it,   the harp sounded terrible. Many people tried it. They agreed that the harp was useless. It was thrown out as rubbish.

    A little girl found the harp. She didn't know how to 2 it. She decided to have a try. She played day and night. The music was never perfect,  3 each time it sounded a little better.

    One day, the harp started to produce beautiful music. In fact, it was a 4 harp. It could be played well by someone if he put in enough effort (努力).

    The king called the girl to the palace. When he saw that she was playing the old harp. He was filled with joy. He made the girl his own private 5.

犯罪历来是国家法律打击的重点。犯罪的最本质特征是（   ）

①函数f（x）的值域为（0，8；

②对任意的n∈N，都有f（2ⁿ）=2^3﹣n；

③存在k∈（ $\frac{1}{8}$ ， $\frac{1}{4}$ ），使得直线y=kx与函数y=f（x）的图象有5个公共点；

④“函数f（x）在区间（a，b）上单调递减”的充要条件是“存在n∈N，使得（a，b）⊆（2ⁿ，2ⁿ⁺¹）”

其中正确命题的序号是（   ）