【单选题】

Bananas are widely believed to grow on trees: this is incorrect. The banana is a plant which finishes all its growth in one year, reaching a height of 30 feet.Bananas have a subterranean (地下的) stem from which come large, green leaves. The plant reaches its maturity in about 18 months.

As the bunches of bananas mature and the fruit develops, they can be propped (支撑) up with poles and covered with blue polyethylene (聚乙烯) bags. These prevent injury, protect against the frost, and speed ripening by increasing heat and humidity.
Once the bananas plant has produced its fruit, the mother plant dies and is replaced by pups (sucker plants). These grow next to the parent and make a new generation of banana plants.
What is the main idea of the last paragraphA．How the banana plant produces its fruit.
B．How a sucker plant is called a pup.
C．The death of mother plants.
D．The growth of sucker plants.