[单项选择]

People traveling long distances frequently have to decide whether they would prefer to go by land, sea, or air. Hardly can anyone positively enjoy sitting in a train for more than a few hours. Train compartments soon get cramped and stuffy. Reading is only a partial solution, for the monotonous rhythm of the wheels clicking on the rails soon lulls you to sleep. During the day, sleep comes in snatches. At night, when you really wish to go to sleep you rarely manage to do so. Inevitably you arrive at your destination almost exhausted. Long car journey are even less pleasant, for it is quite impossible even to read. On motorways you can, at least, travel fairly safely at high speeds, but more often than not, the greater part of the journey is spent on narrow, bumpy roads which are crowded with traffic. By comparison, trips by sea offer a great variety of civilized comforts. You can stretch your legs on the spacious decks, play games, swim, meet interesting people and enjoy good food
A. It is safe because the car usually goes at high speeds.
B. It is monotonous because reading is quite impossible.
C. It is exhausting because you seldom manage to sleep.
D. It is dangerous because the traffic is always too dense.