The most important factor which contributed to the thinning of the Martian atmosphere was probably the
A) blasting of gas into space by impacts
B) loss of the planet's protective magnetic field as it rapidly cooled
C) chemical reactions with surface rocks
D) formation of the polar caps
B
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Elementary particles that experience the weak nuclear force but not the strong force are called
A) leptons. B) hadrons. C) mesons. D) bosons. E) baryons.
Which of the following statements are true about light waves?
a)The higher the frequency, the longer the wavelength. b)The lower the frequency, the longer the wavelength. c)Higher-frequency light travels faster than lower-frequency light. d)The shorter the wavelength, the higher the frequency. e)The lower the frequency, the shorter the wavelength.
An electron gun sends electrons through a region with an electric field of 
for a distance of 2.5 cm. If the electrons start from rest, how long does it take for the electrons to traverse the gun?
A. 1.1 ns B. 1.1 ?s C. 2.2 ns D. 2.2 ?s E. 4.4 ns
The free-fall contraction of a molecular cloud
a. can be initiated by shock waves from supernovae. b. can be initiated by nearby spectral type G stars. c. can be initiated by the rotation of the cloud. d. causes the cloud to become transparent to ultraviolet radiation. e. causes the particles in the cloud to decrease the speed with which they move.