He turned ______ the radio because his father was asleep. [ ]
A. on
B. down
C. up
D. over
答案:B
能与NaOH溶液反应的属于原子晶体的化合物是( )
A.金刚石
B.石墨
C.石英(SiO2)
D.CO2
被叫集中付费业务是指发话人拨一个特别号码至受话用户,()且无需支付话费的一种国际电话业务。