The problem(s) in piggybacking acknowledgement frames is :
A. There is no need to send separate acknowledgement frames
B. It requires more bandwidth
C. To ascertain, how long the data link layer must wait for a packet onto which the acknowledgement is attached
D. Numbers of acknowledgement frames decrease
Choose the correct answer from the options given below :

Explanation

Piggybacking means attaching an acknowledgement to an outgoing data frame instead of sending it as a separate frame. Statements A and D actually describe the benefits of piggybacking (fewer frames needed, reduced acknowledgement-frame count), not problems, and statement B is also wrong because piggybacking reduces bandwidth usage rather than increasing it. The genuine difficulty is statement C: the data link layer must decide how long to wait for an outgoing data frame on which to attach the pending acknowledgement before giving up and sending it alone, since waiting too long risks a timeout at the sender. Hence the correct answer is C only.