For Grade 3 (Royal Conservatory of Music), Prelude (Op.28, n.20) by Frédéric Chopin is a short piece that is only 16 bars long. It starts out slow and then moves into a faster section, before ending on a sustained chord.
In the Royal Conservatory of Music’s Grade examinations, Grade 3 is the second lowest level. Grade 3 tests your ability to play scales in both hands and in any order, with 2.5-3 octave arpeggios (including sevenths). You also need to be able to play chords in multiple keys, broken chords in 3/4 time within the key of C major, have a strong left hand in the chromatic scale, and to play Grade 3 etudes.
After Grade 3 comes Grade 4 which is currently divided into 5 sections. Grade 4 is the end of preparatory and Grade 5 (the current highest level for RCM exams) starts you of at an advanced level (two levels below Conservatories). Grade 5 is divided into four sections.