Read this paragraph from the article "The Ancestors of our Domestic Dog," and think about how the main idea of the article is introduced. The seeming endless contrasts among breeds of dogs may make us hesitate to accept the conclusion that countless naturalists, beginning with Charles Darwin, have drawn: All domestic dogs are descended from a few wild forms--namely, wolves, jackals, and possibly dingos. How can this be? Cats, rabbits, bird, and guinea pigs—all also domesticated—do not appear in such wide variety.

What does the author do to help readers identify the main idea in his article?

He suggests the main idea indirectly by listing examples and evidence.

He repeats the main idea several times throughout the paragraph.

He asks a question that the rest of the article will answer.

He states the main idea directly in the first sentence of the paragraph.