观察以下课文原句并思考黑体部分的功能:
1. The class was difficult.
2. I couldn’t concentrate on the experiment.
3. The lab is new and the lesson was great.
4. I miss my friends from junior high school.
5. I found most of my classmates and teachers friendly and helpful.
6. The guy next to me tried to talk to me the whole time.
7. I just had my first maths class at senior high school.
