Question

what do scientists know about the future of the universe?
what dark matter is made of
why the expansion of the universe is accelerating
that stars will eventually burn out causing the universe to become cold and dark
that galaxies spin much slower than they should based on visible matter

Explanation:

Scientists know that stars have a finite lifespan. As they exhaust their fuel, they will die. Over a very long time - scale, if this continues, the universe would lack the energy from stars (like heat and light), leading to a cold and dark state. This is a well - established concept in astrophysics. Regarding dark matter (option A), its composition is still unknown. The reason for the accelerating expansion of the universe (option B, related to dark energy) is also not fully understood. Option D is more about the current observation of galaxy rotation speeds and the need for dark matter to explain it, not about the future of the universe.

Answer:

C. that stars will eventually burn out causing the universe to become cold and dark