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 from 44 to 50

The authors noted that while other forms of pollution are decreasing, noise pollution has been increasing. This conclusion is reinforced by the fact that there has been an increase in the number of people who have been complaining about excessive noise in the WHO region. Populations that are exposed to high noise levels can be afflicted by other symptoms such as: stress reactions, sleep-stage changes, and clinical symptoms like hypertension and cardiovascular diseases. All these impacts can contribute to premature mortality. It is important to note that these adverse health problems impact all age groups including children and adolescents. In fact, it has been reported that children who live and or study in an area afflicted with noise pollution tend to suffer from stress, impairments in memory and attention as well as difficulty reading. “In Western Europe, the guidelines say, traffic noise results in an annual loss of at least one million healthy years”. Traffic noise is currently ranked second among environmental threats to public health. The danger of noise pollution is more present to us when we are asleep. Because the human ear is so sensitive, it never rests, it is always working, picking up and transmitting sounds for our brains to interpret. This always on working process is where the danger lies, though you may be sleeping, sounds are still being picked up and processed. The most common side effects of this phenomenon are sleep disturbance and tiredness, impaired memory judgment, and psychomotor skills. The other more serious outcomes of this can be the triggering of the body’s acute stress response, which raises blood pressure and heart rate as the body and brain go into a state of hyperarousal. According to the European Environment Agency, at least 10,000 cases of premature deaths from noise exposure occur each year, although incomplete data mean this number is significantly underestimated.

The word it in paragraph 3 refers to _______. A. human ear B. sound C. the danger D. side effect