问题: Whichofthefollowingstatementsbestexpressesthemainideaofthetext?
A: riverscouldchangetheirdrivinghabitsandkeeptheircarsingoodshape.
B:Theimportanceofsavingfuelisseverelyignored.
C:Savinggasisimportantandcouldbedoneinseveralways.
D:Peopleshouldusefewerautomobilesandmakegooduseoftelephone.