下列物质中硫元素化合价最低的是 [ ]
A.S
B.H2SO3
C.H2S
D.H2SO4
答案：C
—Robert is indeed a wise man.
—Oh, yes. How often I have regretted his advice![ ]
A. to take
B. taking
C. not to take
D. not taking
S700K转辙机摩擦连接器，每半年一次，每次正、反向各（）做打滑试验.
A.2s
B.3s
C.4s
D.5～10s
