题目内容
（请给出正确答案）
[主观题]
All of the following are mentioned as examples of mass transit system that could help with
the problem of inadequate public transportation EXCEPT
A．buses.
B．trains.
C．subways.
D．ferries.
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A．二硫化铁
B．四氧化三铁
C．三氧化二铁
D．含水硫酸钙
E．含水硫酸钠
