根据句意和中文注释，写出所给单词的适当形式。
1. It is very important for children to learn to be ________(诚实的).
2. Don't leave the child ________(by oneself) near the river. It's dangerous.
3. It is a________(not useful
)book.so I throw it away.
4. I couldn't ________(相信) my eyes when he came to my home.
5. The Greens will have a ________(令人愉快的) trip because they plan everything carefully.
