20 BB is in no way shortstacked. 10 BB is like, minimum to even consider this.

Given the situation, I'd say AA, KK, QQ.

In a more realistic situation... Short stack at circa ~5BB, my range opens up a lot, but so much of that depends on a lot of factors not discussed here: Position. Reads... and probably most importantly: My Stack Size. You can call the short stack all in with ANY TWO given enough of the other variables and situational consideration being in your favor.... and this applies to tournament play.

In a ring game? No need to gambol against a short stack without a real hand, regardless of his stack size.