Answer:
The stimuli used in Ebbinghaus's experiment were letter D) three-letter nonsense words.
Step-by-step explanation:
In his study, Hermann Ebbinghaus intended to test the effect of association in memory. To do so, he started studying and memorizing lists of words. To avoid using association, he created 2,300 three-letter nonsense words. He then observed how long it took him to memorize those words, how long it took him to forget them, etc. He observed it is easier to memorize something that does make sense and allow association - such as a poem - than it is to memory something without any possibility of association.