Complete the series: BB, CD, DG, EL, (...)

Refer to the following letter series and answer the question that follows. Counting to be done from left to right only. (Left) B G T D F H A K X W E S I C Q M R Y Z O U (Right) How many such vowels are there, each of which is immediately preceded by a consonant and also immediately followed by a vowel?

Which letter will replace the question mark (?) in the given pattern? A D H F I M ? N R