通常酸雨是指：（ ） A．pH低于5.6的降水 B．pH高于5.6的降水 C．p

已知⊙O₁半径为3cm，⊙O₂的半径为7cm，若⊙O₁和⊙O₂的公共点不超过1个，则两圆的圆心距不可能为（　　）

A．0cm

B．4cm

C．8cm

D．12cm

---Hello, may I speak to Jane?      ---_________

A. Who are you?                B. What’s wrong?

C. This is Jane speaking.          C. She is Jane.

环氢流量下降的原因有哪些？

It _____ we had stayed together for a couple of weeks _____ I found we had a lot in common. [ ]

A. was until; when

B. was until; that

C. wasn't until; when

D. wasn't until; that

可表示粉体流动性的大小的是（）.

A、休止角

B、流速

C、内摩擦系数

D、粒径大小