CCommunity
The pattern followed here is:
Take the numerical value of letters, second letter is one more the first letter and third letter is sum of place value of first two letters.
Also, first letter of next term is 2 less than the first letter of first term.
GHO → G + 1 = H, G = 7, H = 8, G + H = 15 → O
EFK → E + 1 = F, E = 5, F = 6, E + F = 11 → K
Same pattern will be followed for DEI : ?,
DEI → D + 1 = E, D = 4, E = 5, D + E = 9 → I
? = B + 1 = C, B = 2, C = 3, B + C = 5 → E
Hence, the missing term is BCE.