Scallops use jet propulsion to move from one place to another. Their shells make them denser than water, so they normally rest on the ocean floor.
If a scallop wishes to remain stationary, hovering a fixed distance above the ocean floor, it must eject water _____ so that the thrust force on the scallop is _____.

a) upward; upward
b) upward; downward
c) downward; upward
d) downward; downward