APCs and Armored Car questions

[J6A]

Well, the definition of tank (page 5) says (in part) "So units that would be excluded would be self-propellef artillery, reconnaissance and APCs, while most tank destroyers would.count, along with engineering vehicles like the British Crab or Crocodile. "

So, based on this, I think that tank is a subset of AFV. The question is how this relates to efficiency and armored cars. The efficiency rules specify AFV, however the scenario book says tanks.