Find the missing letters in the series DW, ?, LO, PK, TG, XC

Answer 1

HS

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The first letter is the position on the alphabet, the second- the position of the letter in reverse order of the first one:
DW=+4 -4
HS=+8-8
LO=+12-12
PK=+16-16
TG=+20-20
XC=+24-24