Correct Answer: GGKC

Solution : Given:
F_HIEH_JDIF_ _JEL

To fill the series we have to divide the series – F_HI / EH_J / DIF_ / _JEL

Let's check each option –
First option: ELFX; F E HI / EH L J / DIF F / X JEL (No repeated pattern has been found )
Second option: GGKC; F G HI / EH G J / DIF K / C JEL (The first letter decreased by 1, the second letter increased by 1, the third letter decreased by 1 and the fourth letter increased by 1 in the given series)
Third option: KGGG; F K HI / EH G J / DIF G / G JEL (No repeated pattern has been found)
Fourth option: FGEL; F F HI / EH G J / DIF E / L JEL (No repeated pattern has been found)

So, the series becomes→FGHIEHGJDIFKCJEL. Hence, the second option is correct.