A rectangular parallelopiped is formed by planes drawn through the points (5, 7, 9) and (2, 3, 7) parallel to the coordinate planes. The length of an edge of the rectangular parallelopiped is 

all of these

Since the parallelopiped is rectangular. Therefore, the lengths of the edges can be obtained by subtracting the corresponding coordinates. Thus, the lengths of the edges parallel to the coordinate axes are

$5- 2 = 3, 7-3 = 4 $ and $9-7=2$