Correct Answer: hmkstrsrm

Solution : Given:
s_trm_ _ _h_ _mmk_ht_ _mk

To fill the series, we have to divide the series – s_trm_ _ / _h_ _mmk / _ht_ _mk
Let's check each option –
First option: hmkstrsmr; s h trm m k / s h t r mmk / s ht m r mk (No repeated pattern has been found.)
Second option: hmksrtsmm; s h trm m k / s h r t mmk / s ht m m mk (No repeated pattern has been found.)
Third option: hkmstrsmm; s h trm k m / s h t r mmk / s ht m m mk (No repeated pattern has been found.)
Fourth option: hmkstrsrm; s h trm m k / s h t r mmk / s ht r m mk (shtrmmk is repeated in the series.)

So, the series becomes→shtrmmkshtrmmkshtrmmk. Hence, the fourth option is correct.