Which of the following summaries accurately states the main idea of the example passage?

the ancients believed that the phenomena we now call supernovas—exploding large stars—were appearances of new stars. however, to specialized computers and powerful telescopes, scientists now know that these events mark the deaths of old stars.

a. supernovas are dying stars.

b. scientists now are using modern tools.

c. ancient people, like modern people, noticed supernovas.

d. ancient people thought they had discovered new stars.