Many fast-growing countries are less concerned with protecti

Many fast-growing countries are less concerned with protecting__against climate change.
A.one B.oneself C.them D.themselves
I'm moving to the countryside because the air there is much fresher than__ in the country.
A.ones B.one C.that D.those
有什么简单的方法分清这几个词?这种题目我老是错