Which letter-cluster will replace the question mark (?) to complete the given series?

MDSA, KERC, ?, GGPG, EHOI

In the word ‘LAVISLY’, replace each vowel with the next letter in the alphabetical series and each consonant with the previous letter in the Alphabetical Series. How many letters occur more than once in this newly formed word?

How many pair of letters are there in the word “BEAUTIFUL” which has as many letters (in both forward and backward direction) between them as they have in English alphabet series?

In the given word ‘MOTIVATION’ if the vowels are changed to the next letters and the consonants are changed to the previous letters as per the alphabetical series, then which letter/letters are repeated more than once?

How many pair of letters are there in the word “EFFECTIVE” which has as many letters (in both forward and backward direction) in between as they have in English alphabet series?