Help With My College Audition (UK)

[Higgins666]

I just recieved my college audition requirements (the audition is next wednesday). The requirements are as follows

All Students Must:
Recognise a given note
Sing a given note
Recognise a chord
Recognise Specific Intervals

Bassists Must Play:
G Riff
Bb Riff
Em Riff
C7 Riff
Em Pentatonic Scale
Walking bass in a given rhythm

Audition Piece Must Be:
Grade 1-3
Well Prepared
Accurate

Now I have a few questions:
As I don't have the best ear, how can I improve this? I'm currently using: http://www.musictheory.net/trainers/html/id90_en.html to try to train my ear.
Are the "riffs" just a riff played in a certain key? Or are then constructed of that specific scale?
What songs are Grade 1-3? I was thinking of doing either "Killing in the Name Of" or "Peace Sells... But Who's Buying?"
Thanks

[Aner Stroz]

ehm.. i don't know about grades 1-3 but killing in the name of and peace sells are both really easy i think i learnd them at the first week of bass playing..how long have you been playing?