Concept:Retention curves show how memory fades over time. They are based on experimental studies of forgetting.Explanation:Hermann Ebbinghaus conducted the first systematic experiments on memory. He tested himself with nonsense syllables and recorded how much he forgot after different time intervals.From his data, he plotted a curve that shows rapid forgetting initially, then a slower decline. This is called the forgetting curve or retention curve.Ebbinghaus was the first to design and describe such curves. No other psychologist among the options is known for this specific work.Answer:A. Ebbinghaus