Given a sentence, add a phrase that indicates past event.
I decided to take the exam
I decided to take the exam, which I had been preparing for a while now.
Complete the following task based on the instruction and optional input provided.### Instruction:
Given a sentence, add a phrase that indicates past event.

### Input:
I decided to take the exam

### Output:
I decided to take the exam, which I had been preparing for a while now.