Answer:
d. feedback
Step-by-step explanation:
The feedback message is an essential part of communication. When two people or parties communicate, a two-way communication develops: The sender or source (In this case, Speaker 1) sends a message to the receiver (Speaker 2), and the receiver sends back a message. This response or reactions that Speaker 2 sends to Speaker 1 is called "feedback".
Without feedback, the communication would be incomplete or ineffective, as Speaker 1 would not be sure if Speaker 1 understood the message clearly, and Speaker 2 would not be able to give back essential information or opinions.