Which description of the expected behavior of a SIP User Agent Client that received a reliable provisional that contains an offer is true? 

Answer options:

A. the UAC must include an answer in a PRACK
B. the UAC must include an answer in a PRACKACK
C. the UAC may include an answer in an ACK
D. the UAC may include an answer in a PRACK
E. the UAC may include an answer in a PRACKACK

A