question: What do astronomers term the stretching of space that causes the distance between galaxies to increase?
distractor3: contracting universe
distractor1: maintaining universe
distractor2: draining universe
correct_answer: expanding universe
support: An inflating balloon is not exactly like the expanding Universe. The surface of a balloon has only two dimensions, while space has three dimensions. But it is true that space itself is stretching out between galaxies like the rubber stretches when a balloon is inflated. This stretching of space, which causes the distance between galaxies to increase, is what astronomers mean by the expansion of the Universe.