The Smiths are at home. Bill is listening to the music. Mother said to her son,

"Bill, Would you please _____ a little, your baby brother is sleeping." [ ]

A. turn off it

B. turn it off

C. turn down it

D. turn it down

为了保证发动机的正常工作和减少（）损失，要求连杆在尽可能小的重量下，达到一定的刚度和强度，所以连杆的杆身大多制成“工”字形断面。

A、热量

B、能量

C、燃料

D、摩擦