0-1 choices at AAA or above
1-2 choices at AAB-ABB
2-3 choices at BBB
1-2 choices below BBB
This is assuming that ABB is the highest set of grades that your teachers think you could get at the end of year 13, this usually will only be forecast at the end of year 12. If these are your typically working at grades then add one grade to each grade range above (eg: BBB becomes ABB)