A diver in the swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his waterproof flashlight

The angle at which the refraction angle of the light radiating from the denser medium to the rarer medium is 90∘
it is known as the critical angle. The event in which lightmovesg from a dense to normal abnormality appears to be restored to the same dense area with an incident angle greater than the critical angle is known as the internal display angle.

The diver is in the swimming pool and wants to show his stress to the person at the edge of the swimming pool with his waterproof flashlight. it will travel in a straight line as it emerges from the water. Thus, a flashlight will not reach the eye of the person at the end of the pool. Therefore, option A. is incorrect.
If the diver makes the beam of the flashlight incident horizontally, the flashlight will travel in a straight line near the visible connector of air and water and thus, will not reach the human eye's edge. option B. incorrect.
If the diver directs the flashlight event with an angle to slightly higher angle than the critical angle then the beam of flashlight will return to the water due to the event of full internal visibility instead of individual access. the eye of the person at the end of the pool. Therefore, option D. is incorrect.
If the diver directs the flashlight at an angle slightly lower than the critical angle then the beam of flashlight also varies from water source to air and will reach the eye of the person at the edge of the swimming pool.
Therefore, the correct option is C.