$\begin{array}{1 1} \frac{1}{m}=\frac{p}{M}-\frac{m_B}{1000} \\ \frac{1}{m}=\frac{p}{m}-\frac{m_B}{1000} \\ \frac{1}{M}=\frac{p}{M}-\frac{M_B}{1000} \\ \text{none of these} \end{array} $