Administrative assistants often answer the phone lines of their supervisors or managers. over time, some callers' voices become familiar and easy to identify or a familiar number appears on a caller id screen. other times, the voice and the caller's number are unfamiliar. what is the correct response to such calls? a. "may i inquire as to why you're calling? " b. "who's this? " c. "that person isn't available right now, may i assist you? " d. "may i ask who's calling ? "