19. Given point $P(9+\sqrt{-a},-3+a)$. Then the quadrant in which point $P$ lies is ( ).
(A) First quadrant
(B) Second quadrant
(C) Third quadrant
(D) Fourth quadrant
19.D.

From $9+\sqrt{-a}>0$, and $a \leqslant 0$, we know $-3+a<0$.