As a result of crossing over, sister chromatids are no longer identical to each other. True Crossing over prevents homologous chromosomes from separating during meiosis I. False For crossing over to occur, homologous chromosomes must align precisely early in prophase I so that nonsister chromatids can exchange corresponding segments of DNA. Crossing over occurs at the ends of chromosomes, rather than near the centromeres.

True Explanation:

if you look up in the top right corner you'll see your current profile picture, click than click "view profile" you'll be able to change it there.

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.