题目内容：
根据下面内容，回答题：In Japan's capital city of Tokyo, earthquake danger limits the height of buildings. The city hasspread out so far and the traffic has become so heavy that it is very difficult to get from one place toanother. The price of land,too,has become very high. All this explains why a group of Japanese landdevelopers came to the conclusion that there was nowhere to go but down. So far they have dug outspace underground for fifteen major shopping centers ,and the underground construction has only begun.What are some of the advantages of shopping and eating underground? Clean ,filtered( ~,,1~ )air is one of them. The city of Tokyo has one of the most serious smog problems in the world. An other advantage is that there won't be traffic accidents as that on the city's busy streets. Still another is the convenience of moving from place to place. You're usually right next to, or even in, a subway station.And you can even spend the night underground if you like. The Kyobashi Station, for example, indown town Tokyo, has a hotel with a bar, restaurant and barbershop.
It is very difficult to get from one place to another in Tokyo because __________. A．the city is so large and so high
B．there is no traffic
C．we don't know the road
D．the city is so large and the traffic is so heavy
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