Which of the following statements is true of reflection nebulae?
A) They have a distinctive blue color.
B) The gases in reflection nebulae are excited to emit photons.
C) The spectrum of a reflection nebula is not the reflected absorption spectrum of starlight.
D) They are produced when a hot star excites the gas to produce an emission spectrum.
Question 2_____ is a series of three nuclear reactions that builds a helium nucleus by adding protons one at a time.
A) The proton-neutron chain
B) The helium proton chain
C) The proton-proton chain
D) The hydrogen-helium chain
Question 3_____ are reactions that join the nuclei of atoms to form more massive nuclei.
A) Endothermic reactions
B) Nuclear fission reactions
C) Nuclear fusion reactions
D) Chemical reactions
Question 4The carbon-nitrogen-oxygen (CNO) cycle works best in temperatures:
A) lower than 10,000,000 K.
B) higher than 16,000,000 K.
C) higher than 11,000,000 K but lower than 12,000,000 K
D) higher than 13,000,000 K but lower than 15,000,000 K
Question 5When the nuclear reactions begin making too little energy in a star, by virtue of the natural thermostat, the star:
A) would expand slightly.
B) would reduce its central temperature.
C) would increase its density.
D) would increase the mass by a factor of 2.
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