From left to right, every four people are a group, and then from right to left, every six people are a group. It is concluded that only when the last person reports 1 at the time of reporting 6 can someone report 3 at the same time. After understanding, they were divided into the same two groups. From left to right, every 12 person is a group. But in the first group, because the last person reported 1 at 6 o'clock, there was only one person.

Moreover, because the last number of 1 in the group of 6 can only be 1 (starting from 1), you only need to add 6 after completing five groups. However, don't forget to add 1 person to the 1 group.

12*5+6+ 1=67 (person)-the largest number of soldiers in this column.

A: This train has a maximum of 67 soldiers.