阅读理解
The Life Cycle
When you plant a seed, does it stay as a seed forever? No! Plants and animals grow and change throughout their lives.
Many plants begin as seeds. As the seed gets what I needs（water, sunlight, and nutrients from the soil）, it begins to grow. The seed turns into a little plant. It keeps growing until it is a full-grown plant. Then the plant makes new seeds, so that new plants can grow even after the plant grows old and dies. Those seeds will then go through their growth process. Because seeds go through this process over and over again, it is called a life cycle. Animals also have life cycles.
A frog begins as an egg. When the egg hatches, it turns into a tadpole. The tadpoles grow legs and arms, and finally grow into adult frogs. The adult frogs lay eggs, so that new frogs can live even after the frog grows old and dies.
A dog's life cycle is a little different than a frog's, because a dog does not start out as an egg. It is born from its mother's belly. The puppy keeps growing and is finally an adult dog. Then the adult dog might have puppies to continue the life cycle!
Insects like caterpillars go through life cycles, too. Caterpillars begin as eggs. When they hatch, they are larvae. The caterpillar becomes a pupa, and inside of the pupa it turns into an adult. The adult is not a caterpillar; it is butterfly! Then the butterfly lays eggs, so that new caterpillars and butterflies can live even after the butterfly grows old and dies.
Plants and animals don't stay the same throughout their lives; they grow and change through their life cycle.