The time of concentration is defined as A. The time taken by rainfall water to run from most distant point of water shed to the inlet of sewer B. The time required for flow of water in sewer to the point under consideration C. Sum of (A) and (B) D. Difference of (A) and (B)

The correct answer is: A. The time taken by rainfall water to run from most distant point of water shed to the inlet of sewer.

The time of concentration is the time it takes for water to flow from the most distant point of a watershed to the inlet of a sewer or other drainage system. It is an important factor in designing drainage systems, as it determines the size and capacity of the system needed to handle a given amount of runoff.

Option B is incorrect because it only considers the time required for water to flow in the sewer. This does not take into account the time it takes for water to flow from the most distant point of the watershed to the sewer inlet.

Option C is incorrect because it is the sum of two incorrect options.

Option D is incorrect because it is the difference of two incorrect options.