Directions: Choose the letter pair that correctly fills the blank in the series.

AX, CV, ET, GR, ?, KP, MN

The correct answer is IP.

To find the missing letter pair in the series AX, CV, ET, GR, ?, KP, MN, we analyze the pattern for the first and second letters of each pair independently.

Step 1: Analyze the pattern of the first letters
The sequence of the first letters is: A, C, E, G, ?, K, M.
Converting these letters to their numerical positions in the alphabet gives:
A = 1, C = 3, E = 5, G = 7, ?, K = 11, M = 13.

Notice that each letter moves forward by 2 positions:

$1+2=3$ (C)

$3+2=5$ (E)

$5+2=7$ (G)

$7+2=9$ (I)

The 9th letter of the alphabet is I.

Step 2: Analyze the pattern of the second letters
The sequence of the second letters is: X, V, T, R, ?, P, N.
Converting these letters to their numerical positions in the alphabet gives:
X = 24, V = 22, T = 20, R = 18, ?, P = 16, N = 14.

Notice that each letter moves backward by 2 positions:

$24-2=22$ (V)

$22-2=20$ (T)

$20-2=18$ (R)

$18-2=16$ (P)

The 16th letter of the alphabet is P.

Conclusion:
Combining the first letter (I) and the second letter (P) gives the missing pair IP.