What is one piece of scientific evidence for human contributions to global climate change?
A) There is no compelling evidence for human contributions to climate change; the correlations do not show what causes them.
B) Humans deplete the ozone layer, allowing more ultraviolet radiation to reach the Earth.
C) Humans burn forests, drive cars, and build power plants that directly heat the planet.
D) Climate models show that extra carbon dioxide contributed by humans is enough to match the temperature data.
E) Humans are responsible for every possible change to the planet, since humans are the only intelligent life forms.
Question 2
At the time the hypothesis was suggested, what major problem was identified with the idea that the Sun was powered by gravitational contraction?
A) This process would power the Sun for only about 25 million years, but geologists already had evidence the Earth was much older than that.
B) This process could not possibly lead to the observed power output of the Sun.
C) 19th century astronomers should have been able to measure the required change in the Sun's size.
D) Contracting objects cool down rather than heat up.
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