Read the paragraph.

Recently, I have noticed that our student body has adopted a practice that should be avoided. Students discard a large amount of uneaten food during lunch. Everything thrown in the trash bins ends up in a landfill, which is a problem because the pollution and gases related to landfills can harm the environment.

The writer uses the first sentence to

point out several effects of the problem.
sum up the importance of the problem.
propose a solution.
express a viewpoint.