A ball valve was found leaking in service. Upon inspection it was found that the PTFE seat had worn out and was renewed. The valve stopped leaking in closed condition. How do you think a ball valve provides perfect sealing?

A. The seat fitted is slightly smaller than the outer dimensions of the ball, thus providing interference fit when closed
B. Either a floating seat is pressed onto trunnion supported ball by liquid pressure or floating ball is pressed onto the seat
C. Ball is not exactly spherical and is shaped such that during closure the surface coming into contact with seat is of slightly bigger diameter providing sealing
D. Seat is not exactly spherical, but slightly tapered so that during closure the ball sits tightly on the seat

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