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Which of the following statements regarding the design flow regime of rainwater pipes on building roofs is in line with the current \"Code for Design of Building Water Supply and Drainage\"? ( ) A. The rainwater drainage from the roofs of high-rise buildings should be designed based on pressure flow. B. The rainwater drainage from the large roofs of industrial plants, warehouses, and public buildings should also be designed based on pressure flow. C. The drainage outside eaves gutters should be designed based on pressure flow. D. The drainage outside long gutters should be designed based on gravity flow. Answer: B. Option A does not comply with the provisions of Article 4.9.10, Paragraph 3, of the current Code for Design of Building Water Supply and Drainage Systems. High-rise buildings have a small catchment area, so gravity-based drainage is sufficient to meet their drainage needs. Moreover, using gravity-based drainage reduces the requirements regarding the pressure resistance of the piping,; therefore, the roof rainwater drainage system in high-rise buildings should be designed based on gravity flow. C does not comply with the provisions of Paragraph 1, Article 4.9.10 of the current Code for Design of Building Water Supply and Drainage. External gutter drainage is commonly used in multi-story residential buildings or ordinary civil buildings. Since these structures have a small roof area and there are multiple drainage outlets around them, gravity-driven drainage is preferred over pressure-driven drainage. D does not comply with the provisions of Paragraph 2, Article 4.9.10 of the current Code for Design of Building Water Supply and Drainage. External drainage systems in long gullies are commonly used in industrial buildings. Due to their large catchment areas, fewer drainage risers can be installed; therefore, pressure flow drainage is employed so as to take advantage of the high water-carrying capacity of the piping system to remove roof rainwater corresponding to a certain return period. Option B complies with the provisions of Paragraph 4, Article 4.9.10 of the current Code for Design of Building Water Supply and Drainage. Industrial buildings, warehouses, and public buildings typically have large catchment areas but few locations where vertical pipes can be installed. Only by making the most of each vertical pipe can roof rainwater be effectively drained; therefore, pressure flow drainage should be employed.