Beta rays can penetrate
A)
air only.
B)
a piece of paper.
C)
several millimeters of aluminum.
D)
several centimeters of lead.
E)
several meters of iron.
C
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A spinning neutron star has been observed at the center of a ________
A) red supergiant B) supernova remnant C) planetary nebula D) protostar
The largest difference between Mars' northern and southern hemispheres is that
A) the northern is higher overall, despite some high volcanoes in the south. B) the northern has all the outflows and must have been much hotter. C) the southern has a polar cap, but none ever forms in the north. D) the southern is much darker, with large mare-like basaltic lava flows. E) the southern appears older, with more impact craters.
The planet with the most prominent rings is
a. Jupiter. b. Saturn. c. Uranus. d. Neptune.
Why can't current theories describe what happened during the Planck era?
A) We do not know how hot or dense the universe was during that time. B) We do not understand the properties of antimatter. C) We do not yet have a theory that links quantum mechanics and general relativity. D) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant.