Concept:The sentence shows a cause-and-effect relationship.
The blank must introduce the reason for Olu's success.
Explanation:Olu passed his examination because he was a determined student.
His determination is the reason for his success.
The correct connective must mean "for the reason that".
"Because" fits this meaning exactly.
"Although" would show contrast.
"Unless" would express a condition.
"When" would indicate time.
Therefore, "because" is the right choice.
Answer:because