5. be obliged to 有义务,必须,强迫 
e.g. parents are obliged to send their children to school. 父母有义务让孩子接受教育. 
The poor girl was obliged to give up her study. 可怜的女孩被迫辍学了. 

6. work on 致力于 
e.g. He is working on the research and development of the latest teaching software. 
他目前正潜心研究最新的教学软件. 
They have been working on promoting the friendship between the two nations. 
他们一直致力于加强两国的友谊. 

7. consist of 包括 
e.g. our class consists of 15 girls and 20 boys.我们班级有15个女生20个男生. 
The team consists of members from different clubs. 
这支队伍的队员来自各个俱乐部.