Question

keenan is a sprinter on his school’s track team. during a race, his breathing rate increases until it is much higher than his resting breathing rate. his breathing rate remains elevated until the race is over. once the race is finished, keenan’s breathing rate gradually returns to normal. which graph could show keenan’s breathing rate during and after a race?

Explanation:

Step1: Analyze the first graph

The first graph has a segment where the breathing rate is constant (horizontal line) after increasing, then a sharp drop, then a gradual decrease. But the problem states the breathing rate remains elevated until the race is over (should be a constant or still increasing? No, the description is: increases until much higher, remains elevated until race over, then gradually returns. Wait, the first graph: let's check the behavior. The problem says: during race, breathing rate increases until much higher than resting, then remains elevated until race over, then gradually returns to normal.

Step2: Analyze the second graph

The second graph: the breathing rate increases (rising line), then when the race ends (the point where it stops increasing), it starts to gradually decrease (the line after the peak is a gradual decrease? Wait, no, the second graph's peak is followed by a line that is part of the decreasing? Wait, no, let's re - read the problem.

Wait, the correct behavior is: increase during race (until much higher), then remain elevated (constant) until race over, then gradually return to normal. Wait, no, the first graph: after the increasing part, there is a horizontal line (remains elevated), then a sharp drop, then a gradual decrease? No, the first graph's later part: the vertical line? Wait, maybe I misread. Wait, the first graph: x - axis is time (sec), y - axis is breathing rate (breaths per min). The first graph has a line that increases, then a vertical drop? No, that can't be. Wait, the second graph: the line increases, then at the peak, it starts to decrease gradually? No, the problem says "remains elevated until the race is over". So the graph should have: an increasing phase (during race), a constant phase (while race is over? No, "until the race is over" means during the race, it increases until much higher, then remains elevated until race ends, then gradually returns. So the graph should have: increase, then constant, then decrease. Wait, the first graph: after the increasing line, there is a horizontal line (constant, elevated), then a vertical line? No, that's not gradual. Wait, maybe the first graph's last part is a gradual decrease after a horizontal line, and the second graph's peak is followed by a line that is part of the decrease without a constant phase.

Wait, the problem says: "During a race, his breathing rate increases until it is much higher than his resting breathing rate. His breathing rate remains elevated until the race is over. Once the race is finished, Keenan’s breathing rate gradually returns to normal."

So the graph should have three phases:
1. Increasing (breathing rate vs time: positive slope)
2. Constant (breathing rate vs time: zero slope, elevated)
3. Decreasing (breathing rate vs time: negative slope, gradual)

Looking at the two graphs:

First graph: The line increases, then becomes horizontal (constant, elevated), then has a vertical drop? No, that's not gradual. Wait, maybe the first graph's last segment is a gradual decrease after the horizontal segment, and the second graph has no horizontal segment (it increases, then immediately starts to decrease, which doesn't match "remains elevated until race over").

So the first graph (top one) has the increasing phase, then a constant phase (remains elevated), then a gradual decrease (the line after the horizontal segment is a gradual decrease? Wait, the top graph's purple line: first it increases, then it's horizontal (constant), then it has a vertical line? No, maybe the grid is misinterpreted. Wait, maybe the first graph (top) has:

- A line with positive slope (increasing during race)
- Then a horizontal line (remains elevated until race over)
- Then a line with negative slope (gradually returns to normal)

The second graph (bottom) has:

- A line with positive slope (increasing)
- Then a line with negative slope (immediately decreasing, no elevated phase)

So the correct graph is the first one (top graph) because it has the increasing, then elevated (constant), then gradual decrease phases.

Answer:

The top - most graph (the first graph with the horizontal segment between the increasing and decreasing parts) shows Keenan's breathing rate during and after a race.