Answer:
ABBB
Step-by-step explanation:
The first bit is sent and read at the same time, and thus, it is "A".
The second bit is sent after 2 seconds, but the reader reads after each second. So, the second, third and fourth terms are all B.
Hence, the overall message is ABBB, and the above option is the correct answer. The others are showing five bits and thus, those options are not the correct ones.