Question about Support Units

[beermonkey]

In order to take certain support units you are required to field 3 Infantry Selections. Is that three full Infantry selections? I mean to say if I have 4 Infantry selections how many Support units can I bring?

Hope this makes sense. I'm still a bit off my game after GenCon.

[Cilionelle]

Three full. Four units gives you the first steps to a second support unit, that's all.