In the early times some people learned    (grow) crops and raise animals for food. They were the first farmers.
Since   (sixteen) century, the word farm has meant agricultural land. But a much older meaning of the word farm is linked  economics. The word farm comes from the Latin word, firma,    means an unchanging payment. Experts say the earliest   (mean) of the English word farm was a yearly payment  (make) as a tax or rent.
Farmers know that   is necessary to make hay while the sun shines. Hay (干草) has to be cut and gathered  it is dry. So a wise farmer never delays gathering his hay when the sun is shining. Rain may soon appear.
A wise person copies the farmer. He works when   (condition) are right. A new mother, for example,   (quick) learn to try to sleep when her baby is quite, even in the middle of the day. If the mother delays, she may lose her chance to sleep. So, the mother learns to make hey while the sun shines.