Test and analysis: it takes 9 minutes for Xiaowen to walk 720 meters, so Xiaowen's moving speed is 720÷9=80(m/t).
In the first 15th minute, Liang Xiao moves 15-9=6 (minutes), and the moving distance is 15×80= 1200 (meters).
∴ The moving speed of Liang Xiao is: 1200÷6=200 (m/t).
∴ 200 ÷ 80 = 2.5, so the speed of Liang Xiao is 2.5 times that of Xiaowen.
When the distance between them is getting closer and closer after 19 minutes, it means that Liang Xiao has reached the finish line, so it is correct for Liang Xiao to arrive at the Youth Palace first;
At this time, the small bright motion is 19-9= 10 (minutes).
The total moving distance is: 10×200=2000 (m),
∴ Xiaowen's exercise time is: 2000÷80=25 (minutes), so the value of A is 25, so 3A = 24 is wrong;
∫ Xiaowen 19 minutes moving distance: 19×80= 1520(m),
∴b=2000- 1520=480, so 4b = 480 is correct.
So the correct ones are: ① ② ④.
So choose B.