In Sperling's Full-Report Procedure, After Viewing a Matrix of Letters

In Sperling's full-report procedure, after viewing a matrix of letters for less than 1 second, what were participants asked to do?

A) listen for a tone, and report only those letters in the row signaled by the tone
B) listen for a tone, and report all letters they could remember from the entire matrix
C) report all letters they could remember from the entire matrix
D) view a second matrix and report only those letters that were in both matrices