In Exercises $37-40$ , locate the absolute extrema of the function (if any exist) over each interval.
$$
\begin{array}{l}{f(x)=\sqrt{4-x^{2}}} \\ {\text { (a) }[-2,2] \quad \text { (b) }[-2,0)} \\ {\text { (c) }(-2,2) \quad \text { (d) }[1,2)}\end{array}
$$