11. For any real number $a$, define $[a]$ as the greatest integer less than or equal to $a$, for example, $[4.9]=4,[5]=5$. If real numbers $x, y$ satisfy $[\sqrt{x}]=9,[\sqrt{y}]=12$, then the maximum possible value of $[x+y]$ is ( ).
(A) 225
(B) 242
(C) 256
(D) 268
(E) 270
$\begin{array}{l}\text { 11. D. } \\ \text { Since }[x]=9,[y]=12 \text {, then } x<100, y<169 .[x+y] \\ <269 \text {. Also, when } x=99.5, y=168.5 \text {, the conditions are satisfied. Thus }[x+y] \\ =268 \text {. }\end{array}$