全电动汽车不使用汽油，但是它们的碳排放情况取决于它们什么时候充电。
All-electric cars use no gas, but their carbon profiles depend on when they plug in.
平均来说，很少有司机知道什么时候给汽车充电最便宜，或者一次充电能开多远。
The average driver knows nothing of when it's cheapest to charge his car battery, or how far he can drive on a single charge.
而臭氧的排放量取决于什么时候你给你的电池插上充电线。
But how much ozone gets produced depends on when you reach for that plug.
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