5.
I might give brainliest pls anwer ASAP!!
Which sentence contains a collective noun?

a. During World War I, messages were tied to pigeon legs.
b. Flags or lights were often used to send messages between ships at sea during World War I.
c. During World War I, people used drums, signals, and lanterns to send messages.
d. Messages can be sent and received in a variety of ways during wartime.