题目内容：
请根据短文的内容，回答题。 Road Politeness
It is all very well to blame traffic jams, the cost of petrol and the quick peace of modern life,but manners on the roads are becoming horrible. You might tolerate the rude and inconsiderate driver, but nowadays the well-mannered motorist is the exception to the rule.
Perhaps the situation calls for a "Be Kind to Other Drivers" campaign; otherwise, it may get completely out of hand.
Road politeness is not only good manners, but good sense, too. It takes the most cool-headed and good-tempered of drivers to resist the temptation to revenge when subjected to uncivilized behaviors. On the other hand, a little politeness goes a long way towards relieving the tensions of motoring. A friendly nod or a wave of acknowledgement in response to an act of politeness helps to create an atmosphere of goodwill and tolerance, so necessary in modern traffic conditions. But such acknowledgements of politeness are all too rare today. Many drivers nowadays don't even seem able to recognize politeness when they see it.
However, improper politeness can also be dangerous. A typical example is the driver who waves a child across a crossing into the path of oncoming vehicles that may be unable to stop in time. The same goes for encouraging old ladies to cross the road wherever and whenever they care to.
A veteran driver, whose manners are faultless, told me it would help if motorists learn to filter correctly into traffic streams without causing the total blockages (堵塞)that give rise to bad temper.
Unfortunately, modern motorists can't even learn to drive, let alone be well-mannered on the road.
Years ago the experts warned us that the car-ownership explosion would demand a lot more give-and-take from all road users. It is high time for all of us to take this message to heart.
According to this passage, troubles on the road are primarily caused by__________. A．the traffic jams.
B．the quick peace of modern life.
C．the cost of petrol.
D．the behavior of the driver.
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