Which of the following explains how to obtain the graph of $y=3-e^x$ from the graph of $y=e^x$?

(a) Reflect the graph of $y=e^x$ about the $y$-axis and then shift this result up 3 unit.
(b) Reflect the graph of $y=e^x$ about the $y$-axis and then shift this result to the right 3 units.
(c) Reflect the graph of $y=e^x$ about the $x$-axis and then shift this result up 3 unit.
(d) Reflect the graph of $y=e^x$ about the $x$-axis and then shift this result to the right 3 units.