社会保障水平=（）/（）*100%。
参考答案：社会保障支出总额、国内生产总值
So much of interest______that most visitors simply run out of time before seeing it all.
A．offers Beijing
B．Beijing offers
C．does Beijing offer
D．Beijing does offer
当加工的孔需要依次进行钻削、扩削、铰削多种加工时，应采用（）。
A.固定转套
B.可换钻套
C.快换钻套
