Answer:
E
Explanation:
There is not enough information in the question. A beat is the observed differences between two frequencies.
Hence, 3 beat represents a difference of 3-hertz between the two frequencies. So the frequency of the piano string could be 1056+3 = 1059-hertz or 1056-3= 1053-hertz.
In order to ascertain the actual value i.e if it is an increase or a decrease in frequency observed, we need more information.