Why does stellar main-sequence lifetime decrease with increasing stellar mass?
A) It doesn't; higher mass stars have more hydrogen available for fusion, and thus have longer lifetimes.
B) Strong stellar winds cause higher mass stars to lose mass quickly.
C) Higher outward pressure prevents the core hydrogen from being replenished by the star's outer layers.
D) Higher core temperatures cause fusion to proceed much more rapidly.
D
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Where was supernova 1987a located?
A) in the Orion Nebula, M-42 B) in Sagittarius, near the Galactic Nucleus C) in our companion galaxy, the Large Magellanic Cloud D) in M-13, one of the closest of the evolved globular clusters E) near the core of M-31, the Andromeda Galaxy
For the wave described by 
, determine the first positive x coordinate where y is a maximum when t = 0.
A. 16 m B. 8 m C. 4 m D. 2 m E. 13 m
Which one of the following objects is most like the planetesimals that formed in the solar nebula?
a. asteroids b. Earth c. Saturn d. Venus e. the Sun
We look toward a cool star. How can we determine that there is an interstellar dust cloud between us and the star?
What will be an ideal response?