You received a great money-saving credit card offer in the mail complete with a rewards program. You read on further to find that the one dollar for every mile spent may not be such a great offer after all since getting a $500.00 airline ticket only happens after you acquire 25,000 miles or spend $25,000. This is a schedule. a) variable-intervalCorrect Responseb) fixed-ratioc) fixed-intervald) variable-ratio