13) A massless rope passes over a frictionless pulley. Particles of mass $M$ and $M + m$ are suspended from the two different ends of the rope. If $m = 0$, the tension $T$ in the pulley rope is $Mg$. If instead the value m increases to infinity, the value of the tension does which of the following?

A) stays constant
B) decreases, approaching a nonzero constant
C) decreases, approaching zero
D) increases, approaching a finite constant
E) increases to infinity
1. **Identify the system and the forces involved:**
   - We have a massless rope passing over a frictionless pulley.
   - Two masses, \( M \) and \( M + m \), are suspended from the ends of the rope.
   - The tension \( T \) in the rope is influenced by the masses on either side.

2. **Recall the formula for tension in an Atwood's Machine:**
   - For an Atwood's Machine with masses \( m_1 \) and \( m_2 \), the tension \( T \) in the string is given by:
     \[
     T = \frac{2m_1m_2g}{m_1 + m_2}
     \]

3. **Apply the formula to the given problem:**
   - Here, \( m_1 = M \) and \( m_2 = M + m \).
   - Substitute these values into the tension formula:
     \[
     T = \frac{2M(M + m)g}{M + (M + m)} = \frac{2M(M + m)g}{2M + m}
     \]

4. **Simplify the expression:**
   - The tension \( T \) can be rewritten as:
     \[
     T = 2Mg \cdot \frac{M + m}{2M + m}
     \]

5. **Analyze the behavior of \( T \) as \( m \) increases:**
   - When \( m \) is very small (approaching 0), the expression simplifies to:
     \[
     T \approx 2Mg \cdot \frac{M}{2M} = Mg
     \]
     which matches the given condition that \( T = Mg \) when \( m = 0 \).

   - When \( m \) increases to infinity, the term \( 2M \) in the denominator becomes negligible compared to \( m \):
     \[
     T \approx 2Mg \cdot \frac{m}{m} = 2Mg
     \]
     Thus, as \( m \) approaches infinity, \( T \) approaches \( 2Mg \).

6. **Conclusion:**
   - The tension \( T \) increases and approaches a finite constant value of \( 2Mg \) as \( m \) increases to infinity.

The final answer is \( \boxed{D} \)