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 have not yet determined what dark matter is made of.
• The reason for the accelerating expansion of the universe (attributed to dark energy) is still unknown.
• Based on current understanding of stellar evolution, stars have finite fuel. Once they burn out (over extremely long timescales), without the energy input from stars (in the form of light, heat etc.), the universe would become cold and dark.
• The fact that galaxies spin faster than expected based on visible matter is an observation that led to the concept of dark matter, but it is not directly about the future of the universe.

Answer:

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