oy the scenery, Sara would spend longhours on the train ______ travel by air

John ____________ his students is playing basketball on the playground

The river is becoming dirtier because the steel factory has put waste into it.—Yes. We must take action to improve the .

__________ some coins ,I think there are only 10 dollars left in my pocket.

下列各句中，加横线的成语使用正确的一项是（ ）