Укажите номер подчеркнутого куска, в котором допущена ошибка.A19. The number of

Укажите номер подчеркнутого куска, в котором допущена ошибка.
A19. The number of school-leavers going on to (1) university have declined (2) since (3) the government introduced higher tuition fees (4).
A20. I had just finished (1) getting me dressed (2) when (3) the doorbell rang and the first guest arrived (4).
A21. The lessons cost me (1) over (2) five hundred of dollars (3), but I consider them a good investment (4).
A22. Because of (1) the illegal transfer of music via the Internet (2), many performers have become worrying (3) that their main source of income will grow smaller (4).
A23. Gerry and Louisa told me (1) last week that they have got tickets (2) for the opera (3) in New York at the weekend (4).
A24. It's no diving board (1) at the swimming pool (2) because (3) it's too shallow (4).