If an intersection is not controlled by signs or signals, you must _______.

Answer: A — Always yield

In the case of an intersection not controlled by signs or signals, you should always yield the right-of-way to any vehicles and pedestrians already in the intersection. This means you should allow them to go first before proceeding. Taking the right-of-way (option B) or making hand signals (option D) are not necessary and could potentially lead to confusion or accidents. Stopping and proceeding slowly (option C) may not always be necessary depending on the flow of traffic, but yielding to other vehicles and pedestrians is always the safest and most courteous option. Therefore, option A is the correct answer.