光杆部分为f9的六角头螺栓，9表示（）。
A.粗糙度
B.精度级
C.热处理
D.表面处理
参考答案：B
— The social worker spent nearly two hours __________ the plan. He said he would discuss with you about it these two days.
— Really? __________ is fine.
A．to look through; Some time
B．to look for; Any time
C．looking at; Some time
D．looking through; Any time
面部发育初步完成是在胚胎发育的第几周（）
A.第3周
B.第5周
C.第8周
D.第12周
E.第14周
