Answer:
Option B,D
Explanation:
After pressing S1 charge on upper plate of C1 is +2CV0
After pressing S2 this charge equally distributes in two capacitors. Therefore charge upper plates of both capacitors will be +CV0
When S2 is released and S3 is pressed charge on the upper plate of C1 remains unchanged (=+CV0 ) but charge on upper plate of C2 is according to new battery (-CV0)