阅读短文，从方框中选择适当的词填空（每词限用一次）

Mike is always very busy on Monday. At 7: 00,   he小题1: breakfast. At 8:00, he 小题2:math. At 9:00  , he has English. He likes English, because it's interesting. In the afternoon, he has music and P.E. After school, he can小题3:the piano. In the evening he likes小题4:story books. Oh , it's time for him小题5:TV now. After that he usually writes to his friend , John on the internet.

力的三要素指的是力的______、______和______．