"Select the statements below that are among the possible reasons we might not receive any response from the message we sent to M13 in 1974.
Choose one or more:
A. The extraterrestrials in M13 received the signal but chose not to reply.
B. There is no technologically advanced life in M13.
C. The extraterrestrials in M13 might not have a receiver pointed in the direction of Earth at the time the message arrives.
D. The extraterrestrials in M13 might not be observing the sky at the exact frequency of our message.
"