Which of the following is the best answer to the question, "Why does the Sun shine?"
A) The Sun initially began making energy through chemical reactions. These heated the interior enough to allow gravitational contraction and nuclear fusion to occur.
B) The Sun initially began generating energy through nuclear fusion as it formed, but today it generates energy primarily through the sunspot cycle.
C) As the Sun was forming, nuclear fusion reactions in the shrinking clouds of gas slowly became stronger and stronger, until the Sun reached its current luminosity.
D) As the Sun was forming, gravitational contraction increased the Sun's temperature until the core became hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
D
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Because the interior of the Earth is ________, the crust is much less dense than the core
Fill in the blank(s) with correct word
Which of the following represents a partial or total decarbonization of our energy supply?
A) switching from natural gas to nuclear power B) switching from coal to natural gas C) switching from oil (petroleum) to natural gas D) All of the above. E) None of the above.
In an attempt to avoid “the bends” which occurs if a diver rises too quickly after having been at great depth in the ocean for a long period of time, a diver should come to the surface relatively slowly. What would the rate of change (in Pa/s) of the water pressure be on a diver in the ocean as he rose at 15 m/min? The density of seawater is 1017 
A. 15 kPa/s B. 2.5 kPa/s C. 250 Pa/s D. 150 kPa/s
A concave spherical mirror with a radius of curvature of 20 cm creates a real image 30 cm from the mirror. How far is the object from the mirror?
A) 20 cm B) 15 cm C) 7.5 cm D) 5.0 cm