Light arriving at a concave mirror on a path through the focal point is reflected
A) back on itself.
B) through the focal point.
parallel to the principal axis.
D through the center of curvature.

Through the focal point parallel to the principle axis

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.