Different dog breeds have been bred by humans from a common ancestor over the past few thousand years. This is an example of
A) natural selection
B) un-natural selection
C) artificial selection
D) artificial insemination
C
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What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure?
A) We think it for purely theoretical reasons, based on calculations showing that the Sun has brightened with time. B) The atmosphere is too cold and thin for abundant liquid water today, yet we see evidence of large areas of flowing water in the past. C) The presence of inactive volcanoes on Mars tells us that there must once have been a lot of outgassing, and hence a thicker atmosphere. D) The fact that parts of Mars have a lot of craters tells us that Mars must once have been much warmer.
If two bicyclists move around a circular track of radius 100 m, at the same speed, 10 m/s, but in opposite directions, then
A. they have equal size accelerations, 1 m/s2. B. they might have different accelerations, depending on whether they have identical mass or not. C. they have opposite accelerations, +1 m/s2 (inward) and -1 m/s2 (outward). D. one has centripetal acceleration of 1 m/s2 and the other has centrifugal acceleration of 1 m/s2.
When a cold front advances under a warm front, this results in a(n)
a. stationary front. b. anticyclone. c. cold front occlusion. d. warm front occlusion.
A beam of light in air is incident on a glass slab at an angle of incidence < 90°. After entering the glass slab, the beam of light
A) does not change its path. B) follows the normal to the glass slab. C) bends away from the normal drawn at the point of contact. D) bends closer to the normal drawn at the point of contact.