For the manometer set up shown in the figure, the pressure difference P A - P B is given by

• A. (?H - ? air )gH
• B. (?H - ?L)gH
• C. (?H - ?L) gH + (?L - ? air ) . g(L - H)
• D. (?H - ?L) gL + (?L - ? air )gH