  The energy of a graph G, denoted by E(G), is defined as the sum of the
absolute values of all eigenvalues of G. It is proved that E(G)>=
2(n-\chi(\bar{G}))>= 2(ch(G)-1) for every graph G of order n, and that E(G)>=
2ch(G) for all graphs G except for those in a few specified families, where
\bar{G}, \chi(G), and ch(G) are the complement, the chromatic number, and the
choice number of G, respectively.
