---Why does Tommy look unhappy ?

--- Because his teacher makes him _______ the classroom all by himself .

A．to clean

B．clean

C．cleans

D．cleaning

油库库存商品在进、销、存过程中数量变化总体现的账目是（）。

（A）库存保管账

（B）油品保管总账

（C）油罐动态分户账

（D）散装油品计量保管