Aspeed time graph shows that a car moves at 20 m/s for 15s. the car's speed steadily decreases until it comes to a stop at 40s. which of the following describes the slope of the speed time graph from 15s to 40s

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium