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. 
     How might volunteering contribute to lower blood pressure? Performing volunteer work could increase physical activity among people who aren’t otherwise very active, says lead study author Rodlescia Sneed, a doctoral candidate in social and health psychology at Carnegie Mellon University. It may also reduce stress. “Many people find volunteer work to be helpful with respect to stress reduction, and we know that stress is very strongly linked to health outcomes,” she says.
     As with any activity thought to improve health, researchers are trying to identify the specific characteristics of volunteering that provide the greatest benefit. For example, how much time would you need to put into volunteer work to lower your blood pressure or live longer? In the Carnegie Mellon study, 200 hours of volunteering per year correlated to lower blood pressure. Other studies have found a health benefit from as little as 100 hours of volunteering a year. Which types of volunteer activities improve health the most? No one really knows. Sneed speculates that mentally stimulating activities, like tutoring or reading, might be helpful for maintaining memory and thinking skills, while “activities that promote physical activity would be helpful with respect to cardiovascular health, but no studies have really explored this.”
     One key for deriving health benefits from volunteering is to do it for the right reasons. A 2012 study in the journal Health Psychology found that participants who volunteered with some regularity lived longer, but only if their intentions were truly altruistic. In other words, they had to be volunteering to help others—not to make themselves feel better.
      The Greek philosopher Aristotle once surmised that the essence of life is “To serve others and do good.” If recent research is any indication, serving others might also be the essence of good health.

The word “It” in paragraph 2 refers to _______.

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