Select the combination of letters that when sequentially placed in the blanks of the given letter series will complete the series. M T _ R M _ Q R _ V Q _ M W _ R M _ Q R

R U M R Q Y Q U M Q R X Q U M R Q X Q U S R Q R

Q U M R Q X

M T Q R / M U Q R / M V Q R / M W Q R / M X Q R 1 is subtracted from the second letter. Q U M R Q X