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$C(t)$ is a differentiable function that represents the rate of calories burned per hour during a 45-minute workout.

Interpret, using correct units, the meaning of $C^\prime(30)$.

The number of calories burned during the first $30$ minutes.

The rate of calories burned per hour after $30$ minutes.

The rate of calories burned per hour during the first $30$ minutes.

The rate at which the number of calories burned per hour is changing in calories/hour/hour after $30$ minutes.