What are the four water sources, referred to as "taps," that sedlak believes will solve our urban water crisis?

Answer:

Local water source, recycled water from sewage treatment plants, water conservation from outdoor water use and generating water from desalinated seawater are the four water sources referred to as "taps," that Sedlak believes will solve our urban water crisis.

Explanation:

David Sedlak is an civil and environmental engineer in USA, who has shared four practical solutions to existing water crisis. His objective is to create a model system where water crises can be minimised by shifting the interest from the current source water supply. He suggested four ways or taps from where water can be obtained in order to prevent occurrence of catastrophic drought due to usage of water from a single source.  

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.