What should come next in the following letter sequence?

A A B A B C A B C D A B C D E A B C D

How many pairs of letters are there in the word 'HORIZON' which have as many letters between them in the word as in the English alphabet ?

If the positions of the third and tenth letters of the word 'DOCUMENTATION' are interchanged, and likewise the position of the fourth and seventh letters, the second and sixth letters, is also interchanged, which of the following will be eleventh letter from the right end ?

How many pairs of letters are there in the word 'PRESENTMENT which have as many letters between them in the word as in the alphabet ?     

How many pairs of letter are there in the word 'BUCKET' which have as many letters between them in the word as in the alphabet ? 

Arrange the following words will come in first if all of them are arranged alphabetically as in a dictionary?

Arrange the following words will come in middle if all of them are arranged alphabetically as in a dictionary?

What word will come in middle if all of the following are arranged alphabetically as in a dictionary?

Donkey, Donator, Donjon, Donate, Donative.