The curve $y=e^{-x}$ is

Question

$$\begin{array}{1 1}(1)concave\;upward\;for \;x>0&(2)concave\;downward\;for\;x>0\\(3)every \;where\;concave\;upward &(4)every\;where\;concave\;downward\end{array}$$