The correct answer is - c. an aging population that the government must support.
China has been trying to discourage the population growth in the country for around half a century now, and while it may be good for lots of reasons considering the size of the country's population, it might affect the economy in the future in a pretty bad way. If this trend continues, it means that relatively soon, China's age demographic picture will change drastically, where the percentage of the old population will constantly grow, thus having an aging population. This population will be taking pensions, and those money go through the government, which means the country will have to provide enormous amount of money each year, and as the time passes, more and more as well, in order to support them. Considering the sheer size of the population of the country, pretty soon we can be talking about a number of 150-200 million people that will be living on state money.
Dune deflation hollows are where wind has removed sand down to a level where a layer of particles too heavy for the wind to move (an armoured surface) stabilises the sand and prevents the surface being lowered further.
A crevasse is a deep, wedge-shaped opening in a moving mass of ice called a glacier. Crevasses usually form in the top 50 meters (160 feet) of a glacier, where the ice is brittle.
a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity.
For continental U.S. the answer is never. Since the earth's rotation axis is tilted 23.5 degrees with respect to its orbital motion around the su, one would have to be less than 23.5 degrees above or below the equator to have the sun pass direclty overhead
