The answer is: (a), (c), (b), as seen in the photograph below, and in an mpeg video by clicking your mouse on the photograph.
Two effects are present here. First, the pressure is dropping along the tube, so in the absence of the venturi constriction the water column would become higher from left to right. In addition, the constriction results in an increase in the speed of the air and a concommitant decrease in pressure, as seen in the photograph and the video.
The next Question of the Week deals with one aspect of this system.
