1.回答why的提问,所以依照上下文的连贯来说,祈使句是不通的
2.have sb.do sth.是固定短语,意思是让某人做某事
3.to的不定式忽然、恩多时候表示将来要做的,所以……
4.have sb.doing sth.也是固定搭配,have...to do 是不存在的
5.Some activists suggest people / (who) have been led to / believe that a lot of dangers to the environment have gone away.suggest sb.(should) do sth.建议某人做某事
6.see sth.done固定搭配,看见某事被做
7.这里应该是they spent happy years happily,宾语是happy years,谓语是spent,happily作状语修饰spent
8.something与supplied是被动关系,所以用过去分词形式
9.lecturer应该是被谈论,因此是被动语态