The main difference between perfect competition and monopolistic competition is that a in perfect competition the prices are set by the government. b in monopolistic competition sellers can profit from the differences between their products and other products. c in perfect competition the buyer is free to buy from any seller he or she chooses. d in monopolistic competition there are fewer sellers and more buyers.

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.

the words "strangest" and "unusual" suggest (:

a. unlikely

for improbable?