Correct Answer: FGVG

Solution : Given:
DE_GYUA_TK_GOAQ_

To fill the series we have to divide the series – DE_G / YUA_ / TK_G / OAQ_
Let's check each option –
First option: FGVA ; DE F G / YUA G / TK V G / OAQ A (No repeated pattern has been found.)
Second option: VGFA ; DE V G / YUA G / TK F G / OAQ A (No repeated pattern has been found.)
Third option: FGVG ; DE F G / YUA G / TK V G / OAQ G (In each part – the first and third letters are decreased by 5, the second letter is decreased by 10 and the fourth letter G is repeated.)
Fourth option: BCHL ; DE B G / YUA C / TK H G / OAQ L (No repeated pattern has been found.)

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