The minimum and maximum diameters of sewers shall preferably be A. 15 cm and 100 cm B. 15 cm and 300 cm C. 30 cm and 450 cm D. 60 cm and 300 cm

The correct answer is A. 15 cm and 100 cm.

The minimum diameter of a sewer is typically 15 cm, while the maximum diameter is typically 100 cm. This is because smaller sewers are not able to carry large volumes of wastewater, while larger sewers are more expensive to construct and maintain.

Option B is incorrect because the maximum diameter of a sewer is typically 100 cm, not 300 cm.

Option C is incorrect because the maximum diameter of a sewer is typically 100 cm, not 450 cm.

Option D is incorrect because the minimum diameter of a sewer is typically 15 cm, not 60 cm.