The drop man holes are generally provided in sewers for____________________?

A. water surface
B. center of pressure
C. center of gravity
D. center of buoyancy
E. none of the above

A. higher surface tension
B. lower surface tension
C. surface tension is no criterion
D. high density and viscosity
E. low density and viscosity

A. pressure
B. temperature
C. density
D. modulus of elasticity
E. absolute temperature