2 . Running is often tiring and a lot of hard work, but nothing beats the feeling you get after finishing a long workout around the track.

But while it’s long been believed that endorphins (内啡肽) —chemicals in the body that cause happiness—are behind the so-called “runner’s high”, a study suggested that there may be more to this phenomenon than we previously knew.

According to a recent study published by a group of scientists from several German universities, a group of chemicals called endocannabinoids (内源性大麻素) may actually be responsible for this familiar great feeling.

To test this theory, the scientists turned to mice. Both mice and humans release high levels of endorphins and endocannabinoids after exercise. After exercising on running wheels, the mice seemed happy and relaxed and displayed no signs of anxiety. But after being given a drug to block their endorphins, the mice’s behavior didn’t seem to change. However, when their endocannabinoids were blocked with a different drug, their runners’ high symptoms seemed to fade.

“The long-held notion of endorphins being responsible for the runner’s high is false. Endorphins are effective pain relievers, but only when it comes to the pain in your body and muscles you feel after working out,” Patrick Lucas Austin wrote on science blog Lifchacker.

Similar studies are yet to be carried out on humans, but it’s already known that exercise is a highly effective way to get rid of stress or anxiety. The UK’s National Health Service even prescribes (开药 方) exercise to patients who are suffering from depression. “Being depressed can leave you feeling low in energy, which might put you off being more active. Regular exercise can improve your mood if you have depression, and its especially useful for people with mild to moderate (中等的) depression,” it wrote on its website.

It seems like nothing can beat that feeling we get after a good workout, even if we don’t fully understand where it comes from. At least if we’re feeling down, we know that all we have to do is to put on our running shoes.

1. What did scientists from German universities recently discover?

A．Working out is a highly effective way to treat depression.

B．The runner’s high could be caused by endocannabinoids.

C．Endorphins may contribute to one’s high spirits after running.

D．The level of endorphins and endocannabinoids could affect one’s mood.

2. Why did the scientists give mice drugs in their experiment?

A．To find what reduces the runner’s high symptoms.

B．To see the specific symptoms of the runner’s high.

C．To identify what is responsible for the runner’s high.

D．To test what influences the level of endocannabinoids released.

3. What does the underlined word “notion” mean?

A．Effect.

B．Goal.

C．Opinion.

D．Question

4. What can we know about regular workouts according to the UK’s National Health Service?

A．They can help ease depression symptoms.

B．They are the best way to treat depression.

C．They only work for those with serious depression.

D．They can help people completely recover from depression.

3 . Training for a marathon (马拉松) requires careful preparation and steady, gradual increases in the length of the runs.     1    , buy the best-fitting running shoes you can find. No one can say which brand will work best for you or feel best on your feet, so you have to rely on your experience and on the feel of each pair as you shop. When you have found shoes that seem right, walk in them for a few days to double-check the fit.     2    . As always, you should stretch (伸展) at least ten minutes before each run to prevent injuries.

During the first week, do not think about distance, but run five minutes longer each day.     3    , it is wise to take a day off to rest. But during the next week, set a goal of at least a mile and a half per run.     4    . After two weeks, start timing yourself.     5    . Depending on the kind of race you plan to enter, you can set up a timetable for the remaining weeks before the race.

A．After six days

B．For a good marathon runner

C．Before you begin your training

D．With each day, increase the distance by a half mile

E．If they still feel good, you can begin running in them

F．Time spent for preparation raises the quality of training

G．Now you are ready to figure out a goal of improving distance and time