城市轨道交通系统车辆配备计划中，备用车辆数一般占车辆运用数的比例是（ ）
A. 10%
B. 20%
C. 30%
D. 40%
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Itisprettywellunderstood______controlstheflowofcarbondioxideinandoutoftheatmospheretoday.
A. that
B. when
C. what
D. how
______hewillbeinthefutureis not knowntous.
A. What
B. That
C. Whether
D. Why
_________wasnotourconcern.
A. Nomatterhowhemightpasstheexamination
B. Whetherhepassedtheexaminationornot
C. Thoughhemightpasstheexamination
D. Whether did he pass the examination or not
ThereasonwhyIplantogois________ifIdon't.
A. becaustshewillbedisappointed
B. thatshewillbedisappointed
C. becauseshewillhavebeendisappointed
D. forshewillbedisappointed
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