题干
Some of the heat near the surface of the earth _____ electricity.
A：is used to making
B：are used for making
C：is used to make
D：are used to make
答案(点此获取答案解析）
C
，从转动的半径为 
．已知主动轮做逆时针转动，转速为n，转动过程中皮带不打滑．下列说法中正确的是（ ）
