Which is the best description of the light paths necessary to see an object? a) light must travel one path from the source to the eye, and another path from the eye to the object. b) light must travel one path from the object to the source, and another path from the source to the eye. c) light must travel one path from the eye to the source, and another path from the source to the object. d) light must travel one path from the source to the object, and another path from the object to the eye.

Option D,  Light must travel one path from the source to the object, and another path from the object to the eye.

Explanation:

In optical physics it has been established that whatever object/things we are able to see is because of the light reflected by the object. Thus, it is clear that either the object must throw light of itself or it should have a source of light whose light can be reflected by object. The reflected light from object then reaches the eye of the viewer and he/she visualizes the object.

Thus, option D is correct.

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.