We don’t go to school _____ weekends.[ ]
A. at
B. on
C. in
D. for
答案：B
An important parents' meeting ________ tomorrow, all the class are busy cleaning the room.
A．given
B．giving
C．will be given
D．to be given
( )是影响铸铁硬度、抗压强度和耐磨性的主要因素。
A．生产工艺
B．基体组织
C．热处理
D．冷却速度
