Final answer:
The metaphors used by Brockriede for unilateral communication are 'Megaphone and receiver', which highlight the one-way nature of the communication process with the sender in control.
Step-by-step explanation:
The correct answer to the question on two metaphors used by Brockriede for unilateral communication is b) Megaphone and receiver. These metaphors represent a one-way form of communication where the message is broadcasted from one party (the megaphone) to another (the receiver), without an anticipated response or interaction from the receiving party. This can be contrasted with reciprocal communication models that involve both parties engaging in a back-and-forth dialogue. In the context of Brockriede's metaphors, this emphasizes the control and coordination the sender has over the communication process, as unilateral communication often serves to inform or direct rather than exchange ideas.