Dizzy Amusement Park is open from $8$:$00$ am till midnight every day of the year. Dizzy charges its patrons a daily entrance fee of $$30$ per person which gives them unlimited access to all of the park's $35$ rides.

For liability insurance, Dizzy pays a set monthly fee plus a small additional amount for every patron entering the park. The cost of liability insurance would best be described as a:

mixed cost

step$-$variable cost

fixed cost

true variable cost