4. Our teacher suggests ________a meeting to discuss about the solution to keep our environment clean.
A. to hold B. hold C. holding D. held
5. Her former leader suggests that she should ________ harder to break her past records.
A. to train B. train C. training D. trained
6. The children volunteer to clean up the local park ________ there are lot of used cans and trash there.
A. but B. because C. and D. so