Error detection is needed because:

A.on channels such as wireless links that are highly reliable, it is cheaper to use an error-detecting code and just retransmit an occasional faulty block

B.it is a basic strategy for dealing with errors, and it allows the receiver enough redundancy to deduce that an error has occurred (but not which error), and have it request a retransmission

C.

error correction is wasteful in terms of the overhead it places on a network, with the large redundancy required to implement it, so simple error detection is the better approach

D.All of the above