In sentence 4 (reproduced below), the writer wants to provide a quotation from Shields that elaborates on the information in sentence 3. Which of the following quotations from Shields best accomplishes this goal?
Shields explains, "You can have a planet that is the right distance from a star but that still isn't habitable, because there are all sorts of other factors that could make it uninhabitable."
a. (As it is now)
b. "We don't want to miss out on discovering life because it uses different chemical processes from life as we know it, or because it is not carbon-based, or because it uses something besides water to carry out molecular processes."
c. "For example, different types of stars emit light in different ranges of the spectrum."
d. "Well, volcanoes can make oxygen—they expel carbon dioxide, which is carbon and oxygen, and that can get broken up by sunlight. So if you detected the oxygen you might think there's life there when there's not."