Q1: 'Cowl' is provided at

ANS:B - upper end of ventilating column

A 'cowl' is typically provided at the upper end of the ventilating column. In sewer systems, ventilating columns are structures used to provide ventilation to the sewer network. They are usually vertical shafts connected to the sewer system, allowing for the exchange of air to prevent the buildup of foul odors and gases. The 'cowl' is a protective covering or hood installed at the upper end of the ventilating column. Its purpose is to prevent rainwater, debris, or other foreign objects from entering the ventilating column while still allowing air to flow freely in and out of the sewer system. So, the correct option is: upper end of the ventilating column.