The source of energy that keeps the Sun shining today is ________.
A) gravitational contraction B) nuclear fusion
C) chemical reactions D) nuclear fission
Question 2
The number of confirmed extrasolar planets
A) is about 600, and is not expected to rise very much.
B) is about 800, and is rising slowly, as observations are quite difficult.
C) was about 800 at the time of publication but is rising rapidly due to new observations by the Kepler spacecraft.
D) has been decreasing as some observations thought to be planets have been disproven.
E) is zero; there are observations thought to be of extrasolar planets but none has yet been confirmed.
