V. Read the following passage and choose the best answers to the questions.

In many ways, the increasingly rapid pace of climate change is a direct result of the growth of the human population. In the last 100 years, the world population has more than tripled. Obviously, this has meant that the world has needed to produce three times as much food, energy, and other natural resources. In addition, the average person uses more energy and natural resources than the average person one hundred years ago, meaning that the rates of consumption are actually much higher than just the increase in population would imply. All of these activities food production, energy usage, and the use of natural resources, contribute to climate change in some way. The greater amounts of oil and other fuels burned to create energy release chemicals which add to global warming. In order to produce more food, farmers cut down trees to gain more land for their fields. In addition, we cut down trees to build the houses needed for a larger population. Those trees are an essential part of controlling global warming. In addition to a growing population, the world also has a population that desires a higher standard of living than in the past, and a higher standard of living requires the use of even more natural resources. For example, China is the world’s most populous nation, with 1.3 billion people. Currently, the standard of living for most of those people is far below that of people in first world nations. Therefore, the average Chinese citizen uses far fewer natural resources and less energy than the average citizen of the US or Japan. If every Chinese person attains a first world lifestyle, the amount of energy and natural resources needed in the world will double, even if the standard of living in every other nation on Earth remains the same as it is today.

They found themselves doing double and sometimes triple (25) _____.