TCP transmission

a) Can a host continue transmitting pure ACKs even after it has sent a FIN flag field in a TCP transmission?

b) What would happen if pure ACKs were also acknowledged?

c) What is the use of CRLF in HTTP?

How do you think TCP would handle the problem if an acknowledgment were lost, so that the sender retransmitted the unacknowledged TCP segment, therefore causing the receiving transport process to receive the same segment twice?