Question about AP physics?

Two parts---
I'm probably taking AP physics C: Mechanics next year, so I was just wondering, There's an AP physics C: Mechanics, and an AP physics C: electricity and Magnetism. But, there's also an AP physics B that isn't separated into two separate subjects...why is that? Is AP physics C just more in depth? Does AP physics cover a more general area of physics?

The second part is, I looked up AP physics books for the AP physics C exams, some books were just AP physics C--the Princeton Review and Barron's, and some books were AP physics B & C--Kaplan's, and the Princeton Review. Kaplan has a good reputation for making books like these, but a lot of the other books are just AP Physics C:--so I'm wondering if I should get the Kaplan, even though I'm just taking AP Physics C---does the Kaplan version go into less detail since it has two portions of physics to cover?