“○”和“●”表示不同元素的原子，下图表示单质的是（   ）

我国石油最大的工业基地是（    ）。   

如图a，小华用20N的力拉着行李箱行走，拉力的方向与水平面成30°.请在b图中画出行李箱所受拉力的示意图.

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.

实验过程中的操作A的名称是____．你认为____（选“甲”或“乙”）组实验方法比 较理想，理由____．