Read the passage and choose the best answer A, B, or C. Happiness is the key to a healthy life. Here are some things you can do to make you happy. Love others fully. When you love somebody, express your love. Don't keep it to yourself. There are many ways to do it. For example, you can say "I love you" more often, do things together, and help them when they need you. You can make yourself and others happy by doing so. Laugh more often. Laughter shows that you are happy, and it has the magic ...

Read the passage and choose the best answer A, B, or C.

Happiness is the key to a healthy life. Here are some things you can do to make you happy. Love others fully. When you love somebody, express your love. Don't keep it to yourself. There are many ways to do it. For example, you can say "I love you" more often, do things together, and help them when they need you. You can make yourself and others happy by doing so. Laugh more often. Laughter shows that you are happy, and it has the magic power of making others happy too. Laughter is like medicine. It helps people live longer. Enjoy adventures, visit a new place, do a new thing, or talk to a new person every week. You will get new knowledge and experience.

The phrase "the key" in the first line is closest in meaning to___