Saying nothing when you lose your train of thought in a presentation is better than trying to cover up.

a. True

b. False

No, I don't think that that's the best strategy.

If you say nothing, you will confuse (or bore) the listeners, and you will make it apparent that you forgot your strain of thought. If you try to cover up, you might actually very likely recover your train of thought or else say something that is valuable to your listeners anyway.