2. Given $\frac{3 x+4}{x^{2}-x-2}=\frac{A}{x-2}-\frac{B}{x+1}$, where $A$ and $B$ are constants. Then the value of $4 A-B$ is ( ).
(A) 7
(B) 9
(C) 13
(D) 5
2. (C).

From $\frac{A}{x-2}-\frac{B}{x+1}=\frac{(A-B) x+A+2 B}{x^{2}-x-2}$, we get $A-B=3, A+2 B=4$.
Thus, $4 A-B=3(A-B)+(A+2 B)=13$.