阅读理解。 There are all kinds of trains in the world. There are trains to carry people, trains to carry animals or carry things. There are fast trains and slow ones. Some trains go through hills. In big cities, the streets are usually very busy. So you can find trains under the ground and trains on a rail above the streets. They carry people quickly in and out of the city. Can a train run over water? Yes, it can. There are many bridges over the rivers. The trains can easily run over the water. But it is not easy to build the bridges. Today's trains have dining-rooms for people. You may eat something in them on the way if you are hungry. Trains are useful to men, women and children. Many children have model trains. With the model trains they can build their own rails and enjoy the wonderful world of trains. 1. There are all kinds of trains. Here 'all kinds of trains' means ______. [     ] A. fast trains and slow trains B. many different kinds of trains C. trains to go through hills D. trains to carry people 2. The trains carry people in and out of the big cities under the ground and on a rail above the streets because ______. [     ] A. the streets are very busy B. the cities are big C. the trains have dining-rooms D. the cities are too small 3. If you are hungry, you may go to ______ of the train to have something to eat when you are travelling by train. [     ] A. some rooms B. some shops C. the dining-room D. the station 4. It's for trains to run over the water but ______ to build bridges. [     ] A. easy, easy B. easily, not easy C. difficult, easily D. easy, difficult