Have you ever taken part in a marathon? A marathon is 42km long. It is the longest race in the world. To make the runner's body work, harder training is quite necessary. A runner should start to prepare for a marathon at least three months before. Preparation may have races, many hours of running at different speeds and changes in diet(饮食). During the training time the runner must eat a fit diet. The diet should have lots of things needed in training the players.In the early days of training, runners run 80km per week. The running is increased every two or three weeks and at least two long runs per week are needed.Two weeks before the marathon, the training program me becomes less, from 100km per week down to 60km and then to 30km in the final week. On the last two days they may not run at all.Breakfast should be eaten at least three hours before the race. Easily digested(消化) food such as cereal(麦), toast(烤面包) and scrambled(捣碎) egg is best, with as much fluid(液体) as possible. Runners should drink water about half an hour before the race to keep up the body fluid.(10.0)(1)、 [单选题] (2.0分)According to the passage, when should a marathon runner begin his training?