Select the Letter Cluster that can replace the question mark (?) in the following series.
ROB, URE, XUH, ?, DAN
Answer & explanation
Correct answer: option 3

Explanation:
ROB, URE, XUH, ?, DAN
The logic followed here is :
R → (+3) → U → (+3) → X → (+3) → A → (+3) → D
O → (+3) → R → (+3) → U → (+3) → X → (+3) → A
B → (+3) → E → (+3) → H → (+3) → K → (+3) → N
So, the letter-cluster that replaces the (?) to complete the series is "AXK"