根据汉语提示写出所缺单词的正确形式。
1. We made a great ______________ (贡献) to protecting our environment.
2. __________ (分开) into three groups, the students began cleaning the classroom.
3. I would hardly believe the news, for I saw him on the street in the __________ (早先的，以前的)days.
4. Take care not to keep your children ____________ (暴露，显露) to bad books.
5. The Forbidden City is one of the world’s greatest works of _____________ (建筑).
6. The football team, ________ (组成) of 22 players and 3 coaches, was set up 3 years ago.
7. He ____________ (不断地) reminded himself of the timetable.
8. My friend was very _______________ (热情的) and he was always ready to help me.
9. Keeping an ____________ (乐观的) state of mind is good for health.
10. Who should be ______________ (负责的) for the accident?