Answer:
B. Variable Interval
Step-by-step explanation:
The variable interval schedule is the schedule in which the schedule is not fixed with regard to anything that means anything can be happen at any time
there is no fixed time
Since in the question it is mentioned that the Professor Bigelow told her students that the quizzes would be provided at non-predictable times so here the surprise quizzes would be reinforced on a variable interval schedule
Therefore the correct option is b.