A student is investigating gravity and falling objects. She drops three balls and times how long it takes each ball to hit the ground. What is the most likely source of error? (1 point)

She used balls that are different sizes.

She did not measure the circumference of the balls.

She dropped the balls from different heights.

She did not measure the mass after the balls hit the ground.

Why is rain likely when warm, moisture-laden air meets cold air? a) the lighter warm air will rise and cool down, causing condensation and rain. b) the cold air moves faster and pushes the warm air away, causing condensation and rain. c) the moisture in the warm air condenses on contact with the cold air, causing rain to fall. d) the cold air mixes with the warm air, reducing its temperature causing moisture to condense.