What event causes the main to hurriedly build a fire a . he falls through the ice b . it begins to snow heavily c . the dog becomes ill d . he goes the wrong way

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.

anxious,the clues in the question suggest he was embarrassed and anxious about boo radley.