Read the sentences below. joanie wants to improve her game. she trains hard every day. in which two ways can the sentences be correctly combined? joanie wants to improve her game, she trains hard every day. because joanie wants to improve her game, she trains hard every day. therefore, she trains hard every day, joanie wants to improve her game. joanie wants to improve her game, so she trains hard every day. joanie wants to improve her game, but she trains hard every day.

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.