For slowly moving objects, the drag force in water is approximately proportional to the speed of the object. The Escherichia coli (E. coli) bacterium propels itself slowly through water by means of long, thin structures called flagella.
If the force exerted on the water by the flagella doubles,
the velocity of the bacterium....

doubles.

does not change.

increases by a factor of four.

decreases by a factor of four.

decreases by half.