5. We always went on ..... holidays when we were young.

Решение:

• book — We always went on book holidays when we were young. (Здесь, скорее всего, имеется в виду 'package holidays' или 'booked holidays'. Из предложенных слов, 'book' может быть использовано в значении 'забронированные').
• catch — We always went on catch holidays when we were young. (Не подходит по смыслу).
• track — We always went on track holidays when we were young. (Не подходит по смыслу).
• monuments — We always went on monuments holidays when we were young. (Не подходит по смыслу).

Ответ: book