Stable, unstable orbit resonances

When I look at

http://neo.jpl.nasa.gov/neo/close.html

I repeatedly finds orbital periods of a whole number of years +/- a
few percent.

I understand that the Kirkwood gap is a resonance phenmomena, i.e.
Jupiter takes so many orbits when any object in the gap takes another
number, and this accelerates any object there away.

I also understand that asteroid 2002 AA29 is in a stable 1:1 resonance
with Earth, which tends to keep it in its orbit, going from one side
of the Earth to the other.

A) Which resonances throws objects away, and which keeps them in place
?

B) How close to perfect resonance do you have to be to assume that
this is a case of resonance, and not just a case of an object in a 2
year orbit ?

C) Is there any other indicators, that are necessary to declare that
this is a case of resonance, and not just a coinsidence ?

Regards

Carsten Nielsen
Denmark