11. Nam will pass the exam if he studies hard. 
12. I had forgotten to lock the door when I drove to the office this morning.

11. Nam will pass the exam. He studies hard (if)
 
=>If Nam studies hard ,he will pass the exam.
 
12. I had forgot locking the door. I drove to the office this morning (when)
 
=>When I drove to the office this morning,I had forgot locking the door.