We usually go to see a doctor when we are ill. Doctors may give us some ________ , and the medicine often makes us feel better. But sometimes the doctor’s medicine doesn’t ________. This happened to one man, Thomas Smith. He was ________ in hospital, but he didn’t get well a few days later. Then he found a new “doctor” inside himself. He saw funny films and read funny books. And something wonderful happened. Laughing ________ his pain after half a year. He could have a good night’s rest. His own happy feeling helped him get well again. He wrote his ________ in his book. He said laughing was very ________. It was the best “medicine”.

Another man, Simon Beck, was also ill, and he had a pain in his back. The doctor couldn’t stop it, so the man imagined his ________ as “a real dog”, and it was hurting him. Then the man talked ________ to the dog. He put his head on the dog’s head and made friends with it. One year later, his pain went away! These stories may ________ you, but more and more people are getting well in this way. So, call on the “doctor” in your ________, and keep happy as well.

“Friends are the family you choose” Do you know why? A new study by Yale University and the University of California San Diego can give us some reasons.

Scientists studied the genes（基因） of almost 2, 000 people. Some of these people were friends, others were simply strangers. Scientists found that friends had more genes in common than strangers. Pairs of friends had similar genes as people do with a distant relative（远亲）. This is about the human genome（人类基因组）. Although l% may not sound like much to geneticists（遗传学）, it is an important number.

“Most people don’t even know who their distant relatives are, yet we are somehow able to choose people who are like our relatives as friends.” Nicholas Christakis, a social scientist at university told Live Science. This might be because similar genes make people visit similar places, or similar genes mean people will have similar skills.

The most common gene that friends have is the “olfactory” gene. It affects（影响）a person’s sense of smell. Imagine that you and someone else both like the smell of trees. You may often visit a park. Therefore, you may likely meet that other person and become friends.

As a result of the study, scientists set an interesting test called the “friendship source”. The test can tell whether two people could be friends by studying their genes.

Do you want to know who will be your friends with the help of the test?