Why is it a good idea not to change the subject line when replying to a message? O so that the reply is sent to the original sender
O so that the reply does not bounce back as undeliverable
O so that the reply matches with the sender's original message
O so that the reply does not inadvertently include unintended recipients

C. so that the reply matches with the sender's original message.

Explanation:

The Sender Message Channel Receiver (SMCR) model of communication was developed and created by David Berlo in 1960. SCMR was developed from the Shannon-Weaver model of communication of 1949.

The SCMR model of communication comprises of four (4) main components and these are;

1. Sender (S): this is typically the source of information (message) or the originator of a message that is being sent to a receiver. Thus, they are simply the producer of a message.

2. Channel (C): this is the medium used by the sender for the dissemination or transmission of the message to the recipient. For example, telephone, television, radio, newspapers, billboards etc.

3. Message (M): this is the information or data that is being sent to a recipient by a sender. It could be in the form of a video, audio, text message etc.

4. Receiver (R): this is typically the destination of information (message) or the recipient of a message that is being sent from a sender. Thus, the receiver is any individual who is able to read, hear or see and process the message being sent or communicated in the communication process.  

Basically, the communication channel used in SCMR must connect the sender with the desired recipients.

Hence, it is a good idea not to change the subject line when replying to a message, so that the reply matches with the sender's original message.