If the side of a square sewer is 1000 mm, the diameter of a hydraulically equivalent circular section, is A. 1045 mm B. 1065 mm C. 1075 mm D. 1095 mm

The correct answer is A. 1045 mm.

The hydraulically equivalent diameter of a circular section is given by the following equation:

$d = \sqrt{4S/\pi}$

where $S$ is the side of the square sewer.

Substituting $S = 1000$ mm into the equation, we get:

$d = \sqrt{4(1000)/\pi} = 1045$ mm

The other options are incorrect because they do not satisfy the equation.