You have decided that you need to improve your study skills and the time you spend reading the textbook. So $,$ ?you set a timer that will go off randomly, between $10$ ?and $30$ ?minutes of reading. When the timer goes off, you can take a break and have a snack. You are using a $\_\_\_\_\_\_$ ?schedule to help with your reading.

?A $.$ ?fixed ratio

?B $.$ ?variable ratio

?C $.$ ?continuous reinforcement

?D $.$ ?fixed interval

?E $.$ ?variable interval