Bicycle license plates in Flatville each contain three letters. The first is chosen from the set $\{C,H,L,P,R\}$, the second from $\{A,I,O\}$, and the third from $\{D,M,N,T\}$. 

When Flatville needed more license plates, they added two new letters. The new letters may both be added to one set or one letter may be added to one set and one to another set. What is the largest possible number of $\text{ADDITIONAL}$ license plates that can be made by adding two letters? 


$ \text{(A)}\ 24\qquad\text{(B)}\ 30\qquad\text{(C)}\ 36\qquad\text{(D)}\ 40\qquad\text{(E)}\ 60 $
1. **Calculate the current number of possible license plates:**
   - The first letter is chosen from the set $\{C, H, L, P, R\}$, which has 5 elements.
   - The second letter is chosen from the set $\{A, I, O\}$, which has 3 elements.
   - The third letter is chosen from the set $\{D, M, N, T\}$, which has 4 elements.
   
   Therefore, the total number of current possible license plates is:
   \[
   5 \times 3 \times 4 = 60
   \]

2. **Determine the effect of adding two new letters:**
   - We need to find the largest possible number of additional license plates that can be made by adding two letters.
   - The optimal strategy is to add both new letters to the set with the fewest elements to maximize the increase in combinations.

3. **Add both new letters to the set with 3 elements:**
   - The set $\{A, I, O\}$ currently has 3 elements. Adding two new letters to this set increases its size to 5 elements.
   - The new number of possible license plates is:
   \[
   5 \times 5 \times 4 = 100
   \]

4. **Calculate the increase in the number of license plates:**
   - The increase in the number of license plates is:
   \[
   100 - 60 = 40
   \]

Conclusion:
The largest possible number of additional license plates that can be made by adding two letters is $\boxed{40}$.