What is the relationship between the velocity of a boat relative to the water and the velocity of the river flow?

A) The velocity of the boat relative to the water is half of the river flow velocity.
B) The velocity of the boat relative to the water is one-third of the river flow velocity.
C) The velocity of the boat relative to the water is twice the river flow velocity.
D) The velocity of the boat relative to the water is half of the square of the river flow velocity.