A3 is printer paper size - larger than the standard A4
A2 milk is a particular type of milk of which the protein of this milk is called A2. It is apparently more easily digestible and “The structure of A2 protein is more comparable to human breast milk, as well as milk from goats, sheep, and buffalo.” A2 milk: Benefits, vs. A1 milk, side effects, alternatives, and more
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.