A continuing unpleasant situation, created when one problem causes another problem that then makes the first problem worse

Explanation:
A vicious cycle is a continuing unpleasant situation in which one problem causes another problem, and the second problem makes the first even worse.

This exactly matches the given definition.
Round cycle – Not a standard English term.
Repetitive cycle – Means something that repeats, but not necessarily in a worsening way.
Vicious cycle – A self-perpetuating negative cycle where one problem worsens another.
Enclosed cycle – Not a standard English term.

Correct Answer: Vicious cycle