If the density of the universe is less than a critical value, thenAnswers:1. it might eventually stop expanding.2. it might continue expanding forever.3. it could expand to a fixed size and remain.4. there's probably less dark matter than luminous.

2. it might continue expanding forever

Explanation:

If the ratio is greater than one, then the actual density of the Universe is greater than the critical density, and thus the Universe will eventually become closed and will ultimately end up collapsing in on itself. If the ratio is less than one, then the actual density is less than the critical density, and the Universe is open and expands forever in every direction

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.

so easy. just google the electromagnetic waves and it’ll pop up.