[单选题]阅读理解  It is all very well to blame traffic jams, the cost of petrol and the quick pace of modern life, but manners on the roads are becoming horrible. Everybody knows that the nicest men become monsters behind the wheel. It is all very well, again, to have a tiger behind the wheel, but to have one in the driver’s seat is another matter altogether. You might tolerate the odd road-hog, the rude and inconsiderate, but nowadays the well-mannered motorist is the exception to the rule. Perhaps the situation calls for “Be Kind to Other Drivers” campaign, otherwise it may get completely out of hand. According to the passage, troubles on the road are primarily caused by（）