Question

Which is a run-on sentence?

If you want to avoid back pain, you should maintain
proper posture.
You must be going somewhere nice your outfit is so
elegant.
On Saturday nights, the roller skating rink plays disco
music.

Answer 1

Hey there!

The correct answer is B.) You must be going somewhere nice your outfit is so elegant.

This is because if it wasn't a run-on sentence, you would use semi-colon between "somewhere" and "nice", but it doesn't, and therefore, is a run-on sentence.

Hope this helps and have a great day! Good luck!