It seems the circuit diagram referred to in the question is missing:

"The equivalent capacitance of the combination shown is"

Without the actual capacitor arrangement, the equivalent capacitance cannot be determined uniquely, because different combinations of identical capacitors $C$ can give different results such as:

• $\frac{C}{2}$
• $2C$
• $\frac{5C}{3}$
• $4C$

What is needed

To solve this step-by-step, I need the figure/circuit diagram showing how the capacitors are connected.

About the stored answer

The stored correct answer is D: $2C$, but without the diagram, there is no way to verify whether that is correct.

So I cannot honestly derive the answer from the information provided alone.