Natalia has a pure culture of E. coli that is in the exponential growth phase at this point her sample contains 640000 E. coli cells if E. coli has a generation time of 1hour how long ago was the number of E. coli cells 80000

b is the correct answer

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.