4 Simple English Sentences:

1. This is a watermelon.这是一个西瓜。
2. A watermelon is very big.西瓜非常非常大。
3. It's green outside and red inside.它外面绿绿的，里面红红的。
4. Tap tap tap - hollow means ripe!拍拍拍，咚咚响就是熟了！