Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

We are a planet of seven billion people, and this number is growing by about 370,000 people every day. This is putting a huge strain on the planet's natural resources. For many governments and environmental organizations, the race is on to drastically reduce our consumption of resources before they run out. Water is one of our most precious resources. Our quality of life, as well as life itself, depends on the availability of clean, fresh water. It is the most widely used resource in industry, and plays a major role in energy production. Although 70 percent of the world is covered in water, only 2.5 percent of that is fresh water, and less than one percent of that freshwater is readily available to us. Yet we often overestimate how much water we have, and reduce it further through pollution or inefficient use. Some 92 percent of all fresh water used annually is dedicated to growing plants and raising animals for food. This means that if water runs out, our food supply might follow. In India, it is estimated that future water shortages could reduce grain harvests by 25%. In a country where the population exceeds 1.2 billion people and is growing rapidly every year, this is a huge concern. India, like many developing countries, is already struggling to provide for its population. While most people in developed countries can get water at the turn of a tap, nearly four billion people elsewhere lack access to safe water, according to United Nations Development Report. Rain forests are another endangered-resource. While rain forests are critically important to humanity, they are rapidly being destroyed by human activities. The biggest cause of deforestation is conversion of forest land for agriculture. Often called the "Lungs of the Planet”, rain forests once covered 14 percent of the Earth's land surface, but this has shrunk to only six percent. Every second, an area of rain forest, the size of a football field, is destroyed at this rate. Rain forests will possibly disappear completely in less than 40 years. (Adapted from: Active Reading)

She came while I ________ my homework. A. have done B. am doing C. was done D. was doing