Which of the following is an example of positive gene regulation?

The tryptophan gene, in which the presence of tryptophan functions as a co-repressor to prevent its own transcription

The lac gene, in which the repressor prevents the synthesis of the enzyme that degrades lactose, is deactivated by the presence of lactose.

CAP, which acts as a required transcription factor for the enzymes that degrade lactose.

All of the above.