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					 Which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?
 _sr_tr_srs_r_srst_
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                        - ttssrr
- tsrtsr
- strtrs
- tstttr
 
Correct Option: D
The given letter series in below pattern.
t sr s tr
After completing the pattern, we will get complete letter series.
t sr s tr/ t sr s t r/ t sr st r
 
	