The correct option is A Promotes thinning of fruits in cherry and walnut
Ethylene is the hormone that promotes fruits ripening. It also promtes the thinning of fruits in cherry and walnut. It is a gaseous hormone, that means a gas that forms through the breakdown of methionine in the cells. It is produced at a faster rate in rapidly growing and dividing cells, especially in darkness.
So, the correct answer is option 'a'.