For the circuit shown, which of the following statements is true ?

Let us consider the first alternative. When switch S1 is closed, the charge on plate 2 will not change because this plate remains isolated. Hence the bound charge on plate will not change. Thus, the potential difference across C1 will remain the same. Similarly, when S3 is closed, V1 and V2 do not change. When S1 and S2 are closed, the charge on plates 2 and 3 will not change. So, the bound charges on plates 1 and 4 will not change. Thus, V1 and V2 remain the same. With S1 and S3 closed, the charge on plate 4 will remain the same. So, the bound charges on plates will not change. Thus, V1 and V2 remain the same.