In each of the following letter series, some of the letters are missing which are given in that order as one of the alternatives below it. Choose the correct alternative.

_ stt _ tt _ tts _

Answer: Option D

Explanation:

The series is tst/tst/tst/tst. Thus, the pattern 'tst' is repeated.

gfe _ ig _ eii _ fei _ gf_ ii

Answer: Option C

The series is gfeii/gfeii/gfeii/gfeii. Thus, the pattern 'gfeii' is repeated.

_ a _ b _ abaa _ bab _ abb

The series is baa/bba/baa/bba/baa/bb. Thus, the pattern baa/bba is repeated.

abca _ bcaab _ ca _ bbc _ a

The series is abc/aabc/aabbc/aabbcc/a.

_ tu _ rt _ s _ _ usrtu _

The series rtus/rtus/rtus/rtus. Thus, the pattern 'rtus' is repeated.