Context: Graph of total rainfall $y$ (cm) vs time $x$ (hours) over a $10$-hour period. Three segments: increasing linearly ($0$–$2$), flat ($2$–$4$), increasing linearly ($4$–$10$).

Answer: D — The rate of rainfall was $0$ centimeters per hour between $x = 2$ and $x = 4$.

Why: From $x = 2$ to $x = 4$, the graph is flat (slope $= 0$), meaning total rainfall did not change. No new rain fell during that $2$-hour period, so the rate was $0$ cm/hr.

Traps:

• A (Rate was $2$ cm/hr between $x = 2$ and $x = 4$): The flat segment has slope $= 0$, not $2$.
• B (Greatest rate between $x = 4$ and $x = 10$): The steepest segment is from $x = 0$ to $x = 2$, not $x = 4$ to $x = 10$.
• C (Rate increased between $x = 0$ and $x = 2$): The rate (slope) was constant during this segment — a straight line means constant rate, not increasing rate.