Which One of the Following Illustrates a Signal in Expository

Which one of the following illustrates a signal in expository instruction?

A) Ms.Allen encourages her students to relate the new material to things they already know.
B) Mr.Ewert's enthusiasm about science is evident in every lecture he presents.
C) Mr.Christiansen gives students a list of the important concepts he will describe in class that day.
D) Ms.Dingwell looks sternly at two whispering students who are obviously not paying attention to the video she is showing.