Select the correct option that will fill in the blank and complete the series.
dmt,fkv,ihy,mdc,……

Let's trace the positional values (A=1, B=2, ..., Z=26) for each letter position across the clusters:
First letter of each cluster:

d=4

f=6 (+2)

i=9 (+3)

m=13 (+4)

Next first letter should be 13+5=18⟹r

Second letter of each cluster:

m=13

k=11 (−2)

h=8 (−3)

d=4 (−4)

Next second letter should be 4−5=−1. In a circular alphabet, −1≡26−1=25⟹y

Third letter of each cluster:

t=20

v=22 (+2)

y=25 (+3)

c=3 (+4) (since 25+4=29≡3)

Next third letter should be 3+5=8⟹h

Combining the letters, we get ryh.