Free lunch. How to answer the next sentence?

This sentence is a western proverb. Considering the living habits of the Middle Ages, breakfast and dinner were very simple, and only Chinese food was their main meal, so proverbs also used lunch as a metaphor.

There is no free lunch in the world, which means that there is no result without paying, and it also reminds people not to be greedy and cheap, and to be vigilant. Nothing for nothing. ? Metaphor means to work hard at everything, and don't think about getting something for nothing.

From a story.

Once upon a time, there was a king who loved his people as much as his son. Under his wise leadership, the people have ample food and clothing and live and work in peace and contentment. The far-sighted king was worried that people would not live a happy life after his death, so he recruited people of insight at home. Command them to find an eternal law that can guarantee people's happiness.

Three months later, the Jinshi presented three six-inch thick silk books to the king and said, "Your Majesty, all the knowledge in the world is concentrated in these three books. As long as people finish reading it, they can guarantee a worry-free life. " The king doesn't think so, because he thinks people don't spend so much time reading books.

So he ordered the class of scholars to continue their studies, and within two months, the scholars simplified three books into one. The king is still not satisfied. A month later, the scholars presented a piece of paper to the king. After reading it, the king said with great satisfaction, "Very well, as long as my people really practice this precious wisdom in the future, I believe they will live a rich and happy life." Say that finish, he gave this class of scholars a heavy reward.

It turns out that there is only one sentence written on this paper: there is no such thing as a free lunch.