5. The current is particularly strong at the point where the river is winding. A number of deaths have occurred there during the past few years. (The number is not stated).
7. Members of the Historical Society have organized a trip to Sunshine Island. Those who wish to go on a trip have to pay an advance of twenty dollars. (Note that, a $20 dollar advance)
9. I'm going to the OR a matinee at the Grand Cinema. A friend of mine has given me a complimentary ticket to the show. (Using 'the' implies the speakers know which 'matinee'; Using 'a' implies the speakers do not know which 'matinee')