砂率减少,会使混凝土的流动性变()。
A、好
B、差
C、不变
D、对流动性没有影响
参考答案:B
— Why does the lake smell terrible?
— Because large quantities of water ____.
A.have polluted
B.is being polluted
C.has been polluted
D.have been polluted
灯具的保护角主要出于考虑( )
A.防止眩光 B.节约能源C.减少照度 D.延长灯具寿命