The graph illustrates the way quantity $P$ changes with quantity $Q$ for a body falling straight down in a uniform gravitational field with air resistance. Which pair of quantities could $P$ and $Q$ stand for?
- A$P$: acceleration, $Q$: force of air resistance
- B$P$: acceleration, $Q$: time
- C$P$: velocity, $Q$: force of air resistance
- D$P$: velocity, $Q$: time