题目内容：

    It turns out that overworking your brain with either physical or mental exercise may lower your ability to delay self-satisfaction. And that may set you up for poor choices in your self-care and finances.

A new study published Thursday in the journal Current Biology asked excellent endurance athletes to overtrain for three out of nine weeks, and compared them to a group who did a normal 9-week training program.

Not only did those overworked athletes perform worse on a cycling test at the end of the overtraining MRls(核磁共振) of their brains during behavioral tasks showed more exhaustion in the cognitive control part of the brain system. “Cognitive control in this situation is the capacity to maintain exercise despite things like muscle pain,” said study author Bastien Blain, a research associate at University College London. “And what we found is that there is an intelligence factor involved in exercising and it has a limited capacity. You cannot use it forever.”

In other words, your brain will burn out and affect your body’s ability to exercise. But that’s not all. Overworking that part of the brain also reduced the athletes’ abilities to resist temptation of an immediate reward, “For example, they were asked whether they preferred $10 now or $50 in six months,” Blain said. “And those who overtrained were more likely to choose the immediate reward, which is interesting. It could provide a mechanism to explain why some athletes are using drugs to improve their performance.”

One caution about the exercise study is that it only looked at endurance athletes, said. Dr. Marc-Andre Cornier, who is associate director of Colorado University’s Anschutz Health and Wellness Center. “This is potentially very important for the higher end athlete who is overdoing it,” Cormier said. “But does this have anything to do with the average Joe going to the gym? You can’t conclude that from this study.”

1.What does the underlined word “it” in the third paragraph refer to?

A.The brain system. B.A limited capacity.

C.An intelligence factor. D.The cognitive control.

2.Why did overworked athletes tend to choose the immediate reward?

A.Because they were too eager to succeed.

B.Because all parts of their brain burned out.

C.Because overtraining led to their bad decisions.

D.Because they took drugs to improve their performance.

3.What is the passage mainly about?

A.A study about self-satisfaction.

B.Negative effects of too much exercise.

C.The relation between brain and exercise.

D.Poor choices in people’s self care and finances.

4.What can we infer from the passage?

A.There is a limit to the brain.

B.Higher end athletes have great potential.

C.Top athletes may suffer from overtraining.

D.Delaying self-satisfaction results in better performance.