A glass U-tube is sealed at one end with the other end being open to the atmosphere. It contains mercury so that the levels in the two sides of the U-tube are the same. The pressure above the mercury in the sealed end is PS and the pressure of the atmosphere is Pat. What can be said about the pressures in this system?
[Figure: U-tube with one end sealed showing PS and other end open showing Pat]
A. PS=Pat
B. The pressure at all points in the mercury is the same
C. PS>Pat
D. PS<Pat