QUOTE(Lemontree @ Aug 25 2009, 05:29 PM)

Thanks @skylark. The only thing, I still don't get is, how it can start on a B. Is there a rule for this? Like, has it to be a dominant or subdominant?
The notes are really only useful as a check, to give you comfort that you've found the right key from the accidentals.
You would expect the opening few notes to be in the key you've identified, and for at least a couple of them to be the notes of the arpeggio (do you learn about tonic triads and dominants/subdominants at Grade 3?).
In this case, you've decided (correctly) that the key is E Major because of the fact that it's got F[C]GD sharps. The arpeggio of E Major is EGB. The starting note is B which is a good sign, and you'll hopefully find that the next couple of notes are also in the arpeggio (although not necessarily). As I said above though, these notes should just be used as a check to give you extra comfort. The main thing is that the accidentals point to the key, not the notes.
If the opening notes are not in the key you think it is, then it should ring alarm bells and you should double check because at Grade 3, I think they normally give straightforward examples.
The opening notes are particularly useful if the accidentals fit more than one key - the opening notes would probably determine which key you would choose.
(Note, I'm just a student so would teachers please correct me if I'm wrong, but I find it helpful myself to write out my understanding - there's nothing like explaining it to someone else to throw up any weaknesses in your own understanding!)