The momentum of the movement slackened in course of time.

The correct answer is D. stopped.

The momentum of a movement is its strength and speed. When the momentum of a movement slackens, it means that it is slowing down and losing strength. This can happen for a number of reasons, such as a lack of interest, a lack of resources, or opposition from others.

Option A, recovered, is incorrect because it means that the momentum of the movement is increasing. Option B, multiplied, is incorrect because it means that the momentum of the movement is growing stronger. Option C, quickened, is incorrect because it means that the momentum of the movement is speeding up.