Your Answer is

Correct Answer is A

Explanation

The first alarm clock rings once every 4 seconds and then every 6 seconds. It can be concluded that it rings once every 4s within 1 minute, and it rings 56/6=9 times in 4s~60s, leaving 2s. , the extra 2s is connected to the second minute, and it can be found that for the second minute, it still rings once every 6s after the first 4s, so it rings 10 times per minute unchanged; similarly, the second alarm clock rings once every 30s after 29s Once, 2 rings per minute remain unchanged; so the total number of rings in t minutes is (10+2)t=12t