Read the sentence. i could tell by the mischievous gleam in their eyes and the sneaky looks they were exchanging that my little brother and sister had been planning to deceive me in some way. the most precise replacement for the underlined word is "arranging preparing conniving organizing."

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.