Given:
- Capacitor C1 is charged to 120 V.
- Capacitor C2 is charged to 200 V.
- When the capacitors are connected together, the potential on each one can be made zero.

To find:
The relationship between the capacitances of C1 and C2.

Solution:
When the capacitors are connected together, they share charge until the potential on each capacitor becomes zero. This means that the total charge on the system is conserved.

Let the capacitance of C1 be C1 and the capacitance of C2 be C2.

Step 1: Finding the charges on the capacitors initially
The initial charge on C1 is given by:
Q1 = C1 * V1
where V1 is the initial voltage on C1 (120 V).

Similarly, the initial charge on C2 is given by:
Q2 = C2 * V2
where V2 is the initial voltage on C2 (200 V).

Step 2: Finding the charges on the capacitors when connected together
When the capacitors are connected together, the total charge on the system is conserved. Therefore, the final charge on the system is zero.

The final charge on C1 is given by:
Q1' = C1 * V1'
where V1' is the final voltage on C1 when the potential becomes zero.

Similarly, the final charge on C2 is given by:
Q2' = C2 * V2'
where V2' is the final voltage on C2 when the potential becomes zero.

Since the total charge on the system is conserved, we have:
Q1' + Q2' = 0

Substituting the expressions for Q1' and Q2' in terms of capacitance and voltage, we get:
C1 * V1' + C2 * V2' = 0

Step 3: Using the given information to find the relationship between capacitances
From the given information, we know that when the capacitors are connected together, the potential on each one can be made zero. This means that V1' = 0 and V2' = 0.

Substituting these values into the equation from step 2, we get:
C1 * 0 + C2 * 0 = 0

Simplifying, we find:
0 = 0

This equation is true for any values of C1 and C2. Therefore, we cannot determine the exact relationship between the capacitances based on the given information.

Conclusion:
The given information does not provide enough information to determine the relationship between the capacitances of C1 and C2. Therefore, none of the given options (a, b, c, d) can be considered as the correct answer.