3. Given that $a$ is a non-negative integer, the equation with respect to $x$
$$
2 x-a \sqrt{1-x}-a+4=0
$$

has at least one integer root. Then the number of possible values of $a$ is ( ).
(A) 4
(B) 3
(C) 2
(D) 1
3. B.

Obviously, $x \leqslant 1$.
Also, $2x + 4 = a(\sqrt{1 - x} + 1) \geqslant 0$, so $x \geqslant -2$. When $x = 1, 0, -2$, $a$ is $6, 2, 0$ respectively; when $x = -1$, $a$ is not an integer.