谁是“协奏曲之父”呢？

You should keep your house _____. [ ]

A. cleaning

B. to clean

C. clean

D. cleans

精削阶梯时，可使用端铣刀的端面刀刃与外圆刀刃分次切削。（）

什么是微格教学

When the Art Gallery was being opened for the public, the Prime Minister was the first entering the gallery following other visitors.

A. was open to... entering the gallery followed with
B. was opened for... to enter the gallery following by
C. was opened to... to enter the gallery followed by
D. was to be opened for... entering the gallery followed with

矿井必须建立专门巷修队伍和设备，巷修工作纳入年度，季度计划。