The correct answer is: B. Provides self cleansing velocity at low discharges.
An egg-shaped section of sewer provides self-cleansing velocity at low discharges because the curved surface of the egg shape helps to keep the water moving in a circular motion. This circular motion helps to prevent sediment from settling on the bottom of the sewer and clogging it.
The other options are incorrect because:
- A. An egg-shaped section of sewer is not necessarily more economical than a circular section. The cost of construction will depend on the specific materials and methods used.
- C. An egg-shaped section of sewer is not necessarily more stable than a circular section. The stability of a sewer will depend on the specific materials and methods used, as well as the soil conditions.
- D. An egg-shaped section of sewer is not necessarily easier to construct than a circular section. The ease of construction will depend on the specific materials and methods used.