original: The larger islands have some fertile valleys and plains.
simplifications: The larger islands has valleys and plains with good soil. The larger islands have some fertile areas. The larger islands have fertile valleys. They also have plains. The larger islands have fertile valleys and plains. The larger islands have some valleys and plains that can grow plants. The larger islands have some valleys and plains where plants grow well. The larger islands have fertile valleys and plains. The big islands can grow more in the valleys and plains. There are fertile valleys and plains on larger islands. The larger islands have a few fertile valleys and plains.