Which of these is true of planetary nebulae?
A) They are the material which causes the eclipses in eclipsing binary systems.
B) They are rings of material around protostars that will accrete into planets in time.
C) They are the envelopes that form when blue stragglers merge.
D) They are expelled by the most massive stars in their final stages before supernova.
E) They are ejected envelopes surrounding a highly evolved low-mass star.
E
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Credit for research in our knowledge of the electron includes
A) William Crookes. B) J.J. Thomson. C) Robert Millikan. D) all of the above E) none of the above
Fusing two carbon nuclei would occur with
A) absorption of energy. B) release of energy. C) neither of these
At any depth in a fluid at rest, the pressure is the same in all directions at the given depth
Indicate whether the statement is true or false
Galaxy collisions were more common in the past
Indicate whether the statement is true or false