guess them.
dont leave questions unanswered.

Yes, if running out of time, you still need to guess...leaving questions unanswered means you didn't finish on time, an extra penalty.

From GMAC:

"Myth – It is more important to respond correctly to the test questions than it is to finish the test.
Reality – There is a severe penalty for not completing the GMAT® test. If you are stumped by a question, give it your best guess
and move on. If you guess incorrectly, the computer will likely give you an easier question, which you are likely to answer
correctly, and the computer will rapidly recover. On the other hand, if you don’t finish the test, your score will be reduced
greatly. Failing to answer five verbal items, for example, could reduce a person’s score from the 91st percentile to the 77th
percentile. Pacing is far more important!"