The graph relates the distance traveled [in miles] to the time elapsed [in hours] on a trip taken by an experimental airplane.  During which hour was the average speed of this airplane the largest?

$\text{(A)}\ \text{first (0-1)} \qquad \text{(B)}\ \text{second (1-2)} \qquad \text{(C)}\ \text{third (2-3)} \qquad \text{(D)}\ \text{ninth (8-9)} \qquad \text{(E)}\ \text{last (11-12)}$
The time when the average speed is greatest is when the slope of the graph is steepest.  This is in the second hour $\rightarrow \boxed{\text{B}}$.