12 students took a group photo, with 4 people standing in the front row and 8 people standing in the back row. Now the photographer will draw two people from the back row and adjust them to the front

12 students took a group photo, with 4 people standing in the front row and 8 people standing in the back row. Now the photographer will draw two people from the back row and adjust them to the front row. If the other relative orders remain unchanged, 2 out of 8 people in the back row ***C82 selection method,

These two people are inserted among the four people in the front row to ensure that the order of the people in the front row remains the same.

Then insert one person from five gaps among four people, and there are five insertion methods;

The rest will be inserted into the gap of five people in the front row.

There are six interpolation methods, ∴6×5.

Then the number of different adjustment methods is C82A62=840. ..

So choose C.