For trunk and out-fall, the type of sewers generally used, is

ANS:C - horse shoe shaped

The "horse shoe shaped" sewer is a type of sewer design that resembles the shape of a horseshoe or an inverted U. It is also commonly known as a "half-round" sewer. This sewer design is characterized by a semicircular cross-section, where the bottom is flat, and the top is semi-circular or horseshoe-shaped. The horseshoe shape provides some advantages over circular sewers in certain situations:

1. Increased Hydraulic Capacity: Horseshoe-shaped sewers can provide a larger hydraulic capacity compared to circular sewers of the same size. This is because the horseshoe shape offers more hydraulic cross-sectional area for a given amount of construction material.
2. Self-Cleaning: The flow characteristics of horseshoe-shaped sewers often promote self-cleaning. The flow concentrates near the bottom, helping to carry solids along and prevent sedimentation and deposition.
3. Ease of Construction: Horseshoe-shaped sewers can be easier to construct compared to circular sewers, especially in certain soil conditions or when dealing with limited access points.
4. Adaptability: They can be more adaptable to changes in flow rates and velocities, as the larger cross-sectional area allows for variations in flow without causing excessive turbulence or surcharge.

Horseshoe-shaped sewers are commonly used in gravity sewer systems, particularly in urban and suburban areas where space constraints or specific hydraulic requirements necessitate alternative sewer designs. However, they may require special attention to design and construction to ensure proper flow characteristics and structural integrity.