Now,in our country free medical treatment covers sickness of

Now,in our country free medical treatment covers sickness of mind as well as ____sickness.
A.normal B.average C.regular D.ordinary
我选D,不确定,A和D咋区分?
Don't leave the water____while you brush your teeth.
A.run B.running C.being run D.to run
我觉得是B,这里是leave sth.加什么词性?可以加动名词的吗?
When first____to the market,these products enjoyed great success.
A.introducing B.intoduced C.being introduced
我选的B,但不知道这是属于什么结构,是非谓语怎么怎么啦?我没系统的学过,大概讲一下就行了