Which sentence from the section "Beyond Our Galaxy" BEST supports the idea that space is mysterious?
A
Our Milky Way galaxy is part of a neighborhood of 54 other galaxies.
B
Without gravity, Earth and everything else in our galaxy would fly off into space.
C
They also thought the stars on the inner orbits should move more slowly because they have less distance to travel.
D
However, dark matter is invisible, and scientists cannot see it with regular telescopes.