公差等级的高低是加工难易、成本高低、使用性能优劣的标志。
参考答案：对
生石灰的化学成分是( )。
A．CaCO3
B．CaO
C．CaC2
D．Ca(O2
A．(A) They bought her a birthday gift,
B．(B) They gave her a farewell party.
C．(C) They surprised her during the party.
D．(D) They saw her off at the airport.
