Practice
The real thing is 20 questions in 45 minutes, and you need 15 right. Every mock here is built to that shape.
A to F share no questions with one another — 120 distinct items between them. Each set is the same test every time you open it, so if you take B today and again next week, the two scores are comparable.
Drawn fresh from the whole bank each time. Use this for extra reps once you have worked through the fixed sets — but judge yourself on the fixed sets, because a random draw is a different test each time.