Select the most appropriate option to fill in the blank.

I am your true friend, ______?

aren’t I

The correct answer is option 4 - aren’t I

The phrase "aren't I" is the correct choice to fill in the blank.

In English, when a statement is made in the positive form ("I am your true friend"), the tag question is typically in the negative form. Hence, "aren't I?" is the correct tag question to follow.