Which of the following is considered a best practice when creating a campaign experiment?

Focus tests on one variable at a time and use separate tests to examine the effects of more than one change.
After an experiment ends, evaluate performance over a timeline that includes the ramp-up period.
When experimenting with creatives, new ads are not subject to ad approvals, so experiments can be expedited.
Pick two or three metrics to evaluate campaign performance and determine the winner of a test.

The correct answer is:

Focus tests on one variable at a time and use separate tests to examine the effects of more than one change.