The photographer drew

For example, A stands on B right and C left, but their order remains unchanged, but students can intervene among them, but generally speaking, A is still on B right and C left, and this order remains unchanged, which is called relative order unchanged.

There are five seats for four people in the front row. For any of the two people drawn out, C5 1 and 1 person, there are now five people, that is, there are six vacancies, of which C61+C61= C62c62 * A22 = A62, so it is C82*A62 in total.