A rubber ball bounces because it is elastic.

There is a law against dropping litter but it is rarely enforced.

Copernicus taught that the earth moves around the sun.

I am going to substantiate this theory.

This subject is outside the scope of our inquiry.

There were a lot of opinions, pro and con, on this question.

This problem baffles me.

How will you dispose of this problem?

This tree is tall, but that one is even taller.

This net here is to keep off mosquitoes.