For \(t\geq 0\) hours, \(H\) is a differentiable function of \(t\) that gives the temperature, in degrees Celsius, at an Arctic weather station. Which of the following is the best interpretation of \(H'(20)\) ?

The 20th hour is represented as the time from \(19\lt t \leq 20\). The rate of change at the end of the 20th hour is an accurate representation of what happens at the end of this interval, or when \(t=20\).

You might be tempted to pick the first or second option, but a better representation of both of these this would be \(H(20)-H(19)\). The average rate would be the same value, just different units.