What Is the Retention Interval in Studies of Forgetting

Multiple Choice

What is the retention interval in studies of forgetting

A)  length of time when the stimulus material is available to be studied by the subjects 
B)  length of time in which the subject has 100 percent recall of the material 
C)  length of time between the presentation of stimuli and the complete forgetting of the information 
D)  length of time between the presentation of stimuli and the measurement of forgetting