A diatomic molecule is made of two masses $m_1$ and $m_2$ which are separated by a distance $r$. If we calculate its rotational energy by applying Bohr's rule of angular momentum quantization, its energy will be given by (n is an integer)

Question

( A ) $\frac{2n^2 h^2}{(m_1 + m_2)r^2}$
( B ) $\frac{(m_1 + m_2)n^2h^2}{2m_1 m_2 r^2}$
( C ) $\frac{(m_1 + m_2)^2n^2h^2}{2m_1^2 m_2^2 r^2}$
( D ) $\frac{n^2 h^2}{2(m_1 + m_2)r^2}$