Two blocks, with masses $M$ and $m$, are connected by a light string that goes over a frictionless pulley, as illustrated. The acceleration of free fall has magnitude $g$. What is the acceleration $a$ of the two blocks?
- A$\frac{M + m}{M - m} g$
- B$\frac{M - m}{M + m} g$
- C$\frac{M}{m} g$
- D$\frac{m}{M} g$