Above DFA is for regular expression $(a+b)^*ab$. All strings end with $ab$.
Complement of DFA accepts all strings does not end with $ab$.
DFA(L') is:
B. String begin with either $a$ or $b$.
$ab$ (string start with $a$) doesn't accept in it reach to nonfinal state $q_2$.
$bab$ (string start with $b$) doesn't accept in it reach to nonfinal state $q_2$.
C. Set of strings that do not contain the substring $ab$
$aba$ (have substring $ab$) does accept in it reach to final state $q1$.
D. The set described by the regular expression $b^*aa^*(ba)^*b^*$
$b$ is string accepted by DFA(L') but above regular expression cannot derive it.
Option A is correct.
DFA (L') accepts all strings that doesn't end with $ab$.