2. If the function $f(x)=\frac{c x}{2 x+3}, x \neq-\frac{3}{2}$, and for all real numbers $x$ except $-\frac{3}{2}$, $f[f(x)]=x$, then $c=$
A. -3
B. $-\frac{3}{2}$
C. $\frac{3}{2}$
D. 3
2. A $f(f(x))=\frac{c^{2} x}{2 c x+6 x+9}=x,(2 c+6) x+\left(9-c^{2}\right)=0, c=-3$