In Experiments on Memorization of Nonsense Syllables, Hermann Ebbinghaus Forgot

In experiments on memorization of nonsense syllables, Hermann Ebbinghaus forgot most of each list within 24 hours, whereas most college students remember about 90% of a list 24 hours later. What accounts for this difference?

A) College students generally learn each list better at the start than Ebbinghaus did.
B) College students have had extensive practice in studying for tests.
C) Ebbinghaus was hampered by proactive interference.
D) Ebbinghaus was hampered by retroactive interference.