Cook : Cook :: Fly : _______
The correct answer is Option A: Flyer.
As, a person who Cook's is a Cook and they cook.
Similarly, someone who flys is a Flyer and they fly.
Option D is the misleading option.
Option C is the past tense of fly, but the corresponding word is cook, so is incorrect
Option B is the present continuous of fly.
Hence Option A is the correct answer.