Hey there,
Your question/statement states: Identify the complete adjective clause. Take this letter that I have written to the post office.
The word [tex]\boxed{adjective \ clause}[/tex] means "to have group of words (with a subject) and also a verb with a great description."
From looking at the sentence above, " Take this letter that I have written to the post office". The group of words that has a subject and also a verb would be (That I have written).The subject would be (that i) and the verb would be (written).
Your correct answer would be (that I have written).
Hope this helps.
~Jurgen
