Answer: D. demographers
Explanation:
When planning for the future of a city, the urban planners need to ensure that the city is able to afford its current and future residents with the facilities needed to provide them with the maximum welfare possible.
To do this the urban planners should reach out to demographers. Demographers study human populations with a view to analyse and ascertain various characteristics such as size, composition, how they are distributed within a geopolitical zone and most importantly, how they will change overtime.
For urban planners to plan for a city that will take care of future residents as well, they would need to know how the kind of future residents they are planning for and this is when they will turn to demographers whose job it is to study and possibly predict future population.
Answer:
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It was caused by a mix of different scenarios. Rome was constantly attacked by Barbarian tribes; they were over-expanded, which made it really hard for them to keep their entire empire under control; they had a lot of economic problems and relied too much on slave labor; and they spent way too much money on their military, just to name a few factors.
During the early earth, when photosynthesis has not yet evolved, there were only negligible amounts of free oxygen in the atmosphere. It was said that the Earth's atmosphere had no free oxygen then. This is about 3.5 billion years ago.