Identify the tense of the given sentence: "I had written a letter to my friend."
The tense of the given sentence "I had written a letter to friend" is Past Perfect tense.
Complete the following task based on the instruction and optional input provided.### Instruction:
Identify the tense of the given sentence: "I had written a letter to my friend."

### Output:
The tense of the given sentence "I had written a letter to friend" is Past Perfect tense.