若u是v的共轭调和函数，则−v是u的共轭调和函数。A. 对B. 错

共轭调和函数的核心在于满足柯西-黎曼方程。若$u$是$v$的共轭调和函数，则存在解析函数$f = u + iv$，此时$u$和$v$满足：
$\frac{\partial u}{\partial x} = \frac{\partial v}{\partial y}, \quad \frac{\partial u}{\partial y} = -\frac{\partial v}{\partial x}.$
题目要求判断$-v$是否是$u$的共轭调和函数，需验证$u$和$-v$是否满足柯西-黎曼方程。通过代入方程可发现矛盾，从而得出结论。

假设$u$是$v$的共轭调和函数，则根据柯西-黎曼方程：
$\frac{\partial u}{\partial x} = \frac{\partial v}{\partial y}, \quad \frac{\partial u}{\partial y} = -\frac{\partial v}{\partial x}.$

若$-v$是$u$的共轭调和函数，则需满足：
$\frac{\partial u}{\partial x} = \frac{\partial (-v)}{\partial y} = -\frac{\partial v}{\partial y}, \quad \frac{\partial u}{\partial y} = -\frac{\partial (-v)}{\partial x} = \frac{\partial v}{\partial x}.$

对比原方程：

1. 原方程$\frac{\partial u}{\partial x} = \frac{\partial v}{\partial y}$，而新方程要求$\frac{\partial u}{\partial x} = -\frac{\partial v}{\partial y}$，矛盾。
2. 原方程$\frac{\partial u}{\partial y} = -\frac{\partial v}{\partial x}$，而新方程要求$\frac{\partial u}{\partial y} = \frac{\partial v}{\partial x}$，矛盾。

因此，$-v$不满足柯西-黎曼方程，不是$u$的共轭调和函数。