2. Given non-zero real numbers $x, 3, z$ form an arithmetic sequence, $x+1, y, z$ and $x, y, z+2$ each form a geometric sequence. Then the value of $y$ is ( ).
(A) 8
(B) 16
(C) 12
(D) 20
2. (C).

From the given information, we can obtain the system of equations $\left\{\begin{array}{l}2 y=x+z, \\ y^{2}=z(x+1), \\ y^{2}=x(z+2) .\end{array}\right.$ From (2) - (3) we get $z=2 x$. Substituting into (1) gives $x=\frac{2}{3} y$. Therefore, $z=\frac{4}{3} y$.
Substituting back into (2) yields the value of $y$ that satisfies the conditions is $y=12$.