ANSWER : abxzy

Explanation : . Abxyz/bxazy/xabyz/abxzy. The block of first five letters is repeated. In each repetition, 1st letter is taken to 3rd place and positions of 4th and 5th letters are interchanged.

ANSWER : rstpq

Explanation : .pqrst/tpqrs/stpqr/rstpq. The last letter of each previous block is taken in the beginning of the successive block.

ANSWER : bcaba

Explanation : . abcde/abcd/abc/ab/a. In each successive blocks the last letter of previous block is dropped.

ANSWER : deabc

Explanation : . abcde/bcdea/cdeab/deabc. In each block 1st letter of previous block is taken to the end of successive block.

ANSWER : xytab

Explanation : . abxyt/tabxy/ytabx/xytab. The last letter of each previous block of five letters is brought in the beginning of the successive block.