如图所示为某一电源的U﹣I曲线，由图可知（   ）

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.

为了营养全面合理，我们每天吃的食物种类应包括：____、____、____、____、____这五大类。

义务教育阶段学校积极心理环境指数调查显示，学校积极心理环境指数每提高10%，学生焦虑、孤独、违规违纪等负面情绪和行为平均降低约6%。这启示我们（    ）