Chemistry Question (precipitate)

Which combination will produce a precipitate?
NaC2H3O2 (aq) and HCl (aq)
AgNO3 (aq) and Ca(C2H3O2)2 (aq)
KOH (aq) and HCl (aq)
NaOH (aq) and HCl (aq)
KOH (aq) and Mg(NO3)2 (aq)

The answer is KOH (aq) and Mg(NO3)2 (aq). I was just wondering if someone could explain why. Thank You!

KOH reacts with Mg(NO3)2 to produce Mg(OH)2 which is insoluble in water - it precipitates
All the other combinations result in products ( if formed) which are all soluble in water.