Assertion (A) : The minimum self cleansing velocity in the sewer, at least once a day, must be generated. Reason (R) : If certain deposition takes place and is not removed, it obstructs free flow and causes further deposition leading to complete blocking of the sewer.

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is not a correct explanation of A
• C. A is true but R is false
• D. A is false but R is true.