1. The researcher immerses oneself in the participants' environment. 2. The aim of the methods to build a theory from the gathered data.
3. This is the portion of the population that is used to represent the entire group
4. A sampling technique chosen by the researcher based in a specific purpose.
5. A researcher chooses a sample that represents specific characteristics.​

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.