How do scientists know dark energy exists? a
We can only detect it by observing the effect of gravity on visible objects.
b
Because the universe we can see is only 4% of what the universe is actually made of.
c
Because it behaves like the opposite of gravity.
d
The observation that all galaxies seem to be moving apart from each other at a faster rate than in the past.

Two people each hold the end of a rope and create waves by moving their arms up and down. this wave is best classified as a transverse wave because a) both the rope particles and the wave are moving in the same direction. b) the wave is moving up and down as the particles of the rope move horizontally. c) the wave is moving horizontally as the particles of the rope move up and down. eliminate d) the wave is moving in a parallel direction with the motion of the person's arms.