①Who jumps highest in your class?

①Who jumps highest in your class?
—john ____.
A.has done B.did C.does D.do
我认为是选B 可答案是选C、 可跳高不已经是过去式了吗?
②Today the forests have almost gone.People must____down too many tress .
A.stop on cutB.stop from cuttingC.be stop to cut D.be stop from cuttingC
③We must do everything we can ____ waste water from running into
rivers.
A.keep B.kept C.to keep D.keeping
can 不是情态动词吗?后面难道不是接原型吗?
④ She counldn't __ her words ___by the students.
A.get understand B.get understood C.make to understand D.make understood
⑤—Shall we ge for a walk this evening?
—Soryy .I'm afraid not .I am too busy ___out.I'm busy __my bike.
A.to go B.going mending C.going to mend D.to go mending
⑥—What should we do to fight A/H1N1 flu?
—We should wash hands often,avoid __to crowded places and so on.
A.go B.going C.gone D.to go
还有就是非谓语动词的那部分知识我不太明白
希望可以帮我讲一下.