Exactly. What you said about that is correct - 2 is the bare minimum (ie, anyone reading this tommorow morning just do two) but for those of you who have prepared, 4 is best 2 from each mandatory and additional.
b0b is right too - comparisons between the pieces in the topic are excellent too, and if you can talk about how they create moods etc. IN RELATION TO THE QUESTION then you are laughing.
If you are stuck for pieces, do the ones you did for your performance. There are many benefits to this - you are very familiar the piece, so you can write out quotes and it makes it easy to make quick study notes within the concept headings.
soulshine - naming basic jazz techniques like use of 7th and 9th chords, syncopation, improvisation, scatting, comping etc is good - its not simplistic at all, it actually lets the marker know that you know what jazz is about. If you can talk about techniques specific to the style of jazz you are analysing too like extreme syncopation in swing or use of traditional orchestral instruments in cool jazz eg. flute or whatever this is good too.
You guys all sound like a bright bunch so I'm sure you you'll do fine tommorow. Best of Luck!!