Rocco and his brother Lou both work in manufacturing plants, but Rocco gets a regular paycheck, whereas Lou is paid according to the number of items he produces. The difference between the way that Rocco gets paid and the way Lou gets paid is the difference between $\_\_\_\_\_\_\_\_$ schedules.

variable interval and variable ratio

variable interval and continuous

fixed interval and fixed ratio

fixed interval and variable ratio

variable interval and fixed ratio