all 1).

1) All AB-->UAB, so DE-->UDE.
2) 1st letter A-B-C from left to right, so 1st letter in the middle is B; A stand at 1, 3, 2nd position, so;
3)  Middle on is from the truncation of the first 2 letters from both left and right words and with order switched, so got 1) too.