Correct Answer: RUDSTUF

Solution : Given:
S_UCTSR_ _ T_RUE_SR_ _T

To fill the series we have to divide the series – S_UCT / SR_ _ T / _RUE_ / SR_ _T
Let's check each option –
First option: RUESTVG ; S R UCT / SR UE T / S RUE T / SR VG T (No repeated pattern has been found.)
Second option: RVDSTUF ; S R UCT / SR VD T / S RUE T / SR UF T (No repeated pattern has been found.)
Third option: RUDSTUF ; S R UCT / SR UD T / S RUE T / SR UF T (Add 1 to the place value of the fourth letter of each part→C + 1 = D; D + 1 = E; E + 1 = F. The remaining letters SRUT is repeated in the series.)
Fourth option: RVESTUF ; S R UCT / SR VE T / S RUE T / SR UF T (No repeated pattern has been found.)

So, the series becomes→SRUCTSRUDTSRUETSRUFT. Hence, the third option is correct.