Select the combination of letters that when placed from left to right in the same sequence in the blanks of the given series will complete the series.
XY_YZ_ _ XYY _ _ ABXY _ _ ZAB _ _ YYZA _

Correct option is D

Given  = XY_YZ_ _ XYY _ _ ABXY _ _ ZAB _ _ YYZA _

using option a, we get YABYZYYXYY

XYYY/ ZA B/  XYY Y/  Z AB/ XY Y Y/  ZAB / X Y YY/ ZA Y

Last term should be ZAB so this does not follows.

using option a, we get  YZBYZYYXYB

XYYY/ ZZ B/  XYY Y/  Z AB/ XY Y Y / ZAB / X YYY/ ZA B

Second term should be ZAB so this does not follows

using option c. XABYZYYXYB

XYZY/ZA B/ XYY Y/ Z AB/XY Y Y/ ZAB/ X Y YY/ZA B

First term should be XYYY so this does not follows.

option d - YABYZYYXYB

XYYY/ ZA B / XYY Y / Z AB/ XY Y Y/  ZAB / X Y YY / ZA B

This perfectly repeat XYYY and ZAB alternatively.

so option d is correct answer.