Answer:
b. retroactive interference
Explanation:
In psychology and memory processes the term retroactive interference makes reference to the phenomenon where you forget previously learned information due to the learning of new information. In other words, this new information interferes with your earlier process of learning and you forget old memories.
In this example, Milton just learned the combination for his new locker but know he is unable to remember the combination for his year-old bicycle look. We can see that the new information (the combination of the locker) interfered with his old memories (the combination of his year-old-bicycle). Thus, Milton is experiencing the effects of retroactive interference.