SS7E型电力机车蓄电池组由（）蓄电池串联而成。
A、24个
B、30个
C、48个
D、50个
参考答案：C
The computer was one of the greatest _ in the 20th century. [ ]
A. invent
B. inventing
C. inventions
D. invention
试述皮肤的基本生理功能。
