Quite a key correct explanation.

The key is an idiom, which means you can know that autumn is coming by the change of a leaf. This idiom vividly expresses the meaning that the development and change of things can be predicted by some subtle signs. The specific explanation is as follows:

1, the origin of this idiom can be traced back to ancient documents in China. The earliest record can be found in "Huai Nan Zi Shuo Shan Xun": you can know the end of the year when you see a leaf fall. It means that when you see a leaf fall, you can know that the year is coming to an end and autumn is coming.

2. Tang Geng, a poet in the Tang Dynasty, also used this idiom in Luwen: One mountain and one monk don't know the number of jiazi, and one leaf knows the autumn on earth. This means that the monks in the mountains don't know how to calculate the Jiazi calendar, but through the fall of a leaf, they can know that the world is about to enter autumn.

This idiom means not only to predict the arrival of autumn by observing the changes of leaves, but also to predict the development and changes of things by observing some subtle signs of things. This ability to observe and predict is very important in life, which can help us better grasp the development trend of things and make more informed decisions.

Knowledge about autumn

Autumn is a season full of rich colors and changes. In autumn, nature begins to gradually transition from lush summer to cold winter. The autumn climate is characterized by cold weather and low temperature. In autumn, the temperature difference between day and night usually increases, and the air becomes relatively dry.

2. Autumn is the harvest season, and it is also the season for many animals and plants to prepare for hibernation. In autumn, leaves will gradually change color, from green to yellow, orange and red. The scenery at this time is very beautiful, which is a good opportunity for travel and photography. Autumn food is very rich, including all kinds of fruits, vegetables and grains.

In autumn, people usually harvest apples, grapes, pumpkins, corn and other fruits and vegetables. In addition, autumn is also a good time to store winter food, and many animals will start to store food for winter needs. There are many outdoor activities in autumn, such as enjoying red leaves, having picnics, barbecues and picking fruits.