Which statement is true about black dwarfs?
a. none currently exist in the universe.
b. they are very hot and massive.
c. they burn brightly for only a few weeks or months.
d. they form after supernova explosions.

Currently, there are no black dwarfs that exist in our universe. Black dwarfs are extremely cool and are almost invisible. They are hypothetical in existence. 

Answer: it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.explanation:   we have equation of motion ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/sso it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.