人工制备煤样时，在破碎到粒度小于（）之前，应用磁铁将煤样中铁屑吸去。
A、3mm
B、02mm
C、1mm
参考答案：B
新生儿在上腭中线和齿龈部位有散在黄白色、碎米粒样颗粒，称为（）
A.马牙
B.板牙
C.螳螂子
D.口疮
E.鹅口疮
After years of overwork, my father’s health ____ and he had to retire from business.
A．broke out.
B．broke up.
C．broke down.
D．broke off.
