When focusing on low power which knob is used to get a clear image

Two knobs are used to get a clear image on low power. The coarse adjustment knob is used to make drastic changes to the image, and the fine adjustment knob is used to make small adjustments to the image. The reason two knobs are used is because you are supposed to get as clear an image as possible on low power before moving on to the next power, and same with medium power.

The answer for this question is c