As per given question, the letter series is following the below pattern.
a a b b
Using the same pattern, we will get complete letter series.
a a b b /a a b b/a a b b/ a a b b

The given letter series in below pattern.
a cc
After using the pattern the complete letter series will be as below.
a cc / a a c / a c c / a a c

The given letter series in below pattern.
a c d
After completing the pattern, we will get complete letter series.
a c d / b d e / c e f / d fg / e g h

The given letter series in below pattern.
a a b a b
After using the pattern the complete letter series will be as below.
a a b a b/ a a b a b/ a a b a b

The given letter series in below pattern.
r t sr
After using the pattern the complete letter series will be as below.
r t sr / r tsr / rt s r / r t sr

The given letter series in below pattern.
ab c
After completing the pattern, we will get complete letter series.
ab c /abc/ a bc/ a bc /a b c
Hence , required answer is caab .

The given letter series in below pattern.
w a x
Using the same pattern, we will get complete letter series.
w a x/ w a x/ w a x/ w a x/ w a x

The pattern of given letter series is :-
m a n
Using the same pattern, we will get complete letter series.
m a n/ m a n/ m a n / m a n/ m a n

As per given question, the letter series is following the below pattern.
a a b b a b b a
After using the pattern the complete letter series will be as below.
a a b b a b b a / a a bb a a ba

As per given question, the letter series is following the below pattern.
c a b ba c
Using the same pattern, we will get complete letter series.
c a b ba c/ ca b b a c/ c ab b ac