Which of the following terms will replace the question mark (?) in the given series?
ADO, DGR, GJU,?

The correct option is JMX.

Let's analyze the given letter series step-by-step to understand the pattern. The series is:
ADO, DGR, GJU, ?

Each term in the series consists of three letters. Let's examine the behavior of each letter position (first, second, and third) across the terms.

1. First Letter Analysis:
The first letters of the terms are: A, D, G, ...
Let's look at their positions in the English alphabet (A = 1, D = 4, G = 7):
A (+3) → D
D (+3) → G
Following this pattern, the next first letter should be:
G (+3) → J (which is the 10th letter of the alphabet)

2. Second Letter Analysis:
The second letters of the terms are: D, G, J, ...
Let's look at their positions in the English alphabet (D = 4, G = 7, J = 10):
D (+3) → G
G (+3) → J
Following this pattern, the next second letter should be:
J (+3) → M (which is the 13th letter of the alphabet)

3. Third Letter Analysis:
The third letters of the terms are: O, R, U, ...
Let's look at their positions in the English alphabet (O = 15, R = 18, U = 21):
O (+3) → R
R (+3) → U
Following this pattern, the next third letter should be:
U (+3) → X (which is the 24th letter of the alphabet)

Combining these letters, we get the next term in the series: JMX.