Answer
M and N
Step-by-step explanation
There are 26 alphabetic letters.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
The half of 26 is (26 × 1/2) = 12 1/2.
This means there are 2 alphabets that are a mid-way.
A B C D E F G H I J K L / M N / O P Q R S T U V W X Y Z
M and N are the two alphabets that are at halfway through the alphabets.