While reading about George Sperling's research investigating visual sensory storage, Umar is surprised to find out that one particular factor caused a significant decline in participants' ability to remember what was seen. What was this factor?a. a longer delay between when participants saw the three rows and when they had to report one of them b. a decrease in the number of items participants had to report, from 12 to 4 letters c. an increase in the amount of time participants could initially see the three rows of four letters telling the participants which of three rows of letters d. they would be asked to remember before the experiment