A.浓硫酸
B.氢氧化钠溶液
C.水
D.饱和食盐水
答案:B
—I have a birthday party this evening. Are you free?
—Yes, I am.
A.Are...busy
B.Do...have time
C.Are...great
D.Do...have homework
在切断刀两个刀尖处各磨一个小圆弧过渡刃的主要目的是()。