Answer:
An exterior angle of the triangle ABC would be ∠1.
Step-by-step explanation:
Exterior Angles: (See attached image)
Lets say you had a polygon (such as the triangle ABC) and you were to take two adjacent sides of that polygon. Lets call the side a and side b. If you were to extend side a, make a y-ish shape between side b and the extended side a. The angle between side b and the "new" part of side a would be the exterior angle.
(See attached image for better understanding.)
Using this, we can find all of the exterior angles of the triangle ABC. They would be ∠1, ∠3, ∠6, ∠8, ∠9, ∠11.
If we look at the answer choices, we will see that ∠1 is one of the answer choices, making ∠1 the solution to this question.
I hope you find my answer helpful. :)