The *blank* of the line on a velocity vs. time graph represents acceleration

Aweather forecaster uses doppler radar to predict the track of a storm near the town of meadowlands. when the doppler signal is pointed at the storm from the town's center, the frequencies of the waves appear to be decreasing. what should the weather forecaster predict? a. that the storm will move around the edges of meadowlands without hitting the tosis center o b. that residents should be prepared, because it is impossible to know whether the storm will hit o c. that the storm is moving toward meadowlands and that residents should be prepared d. that the storm is moving away from meadowlands and is not likely to hit the town