Questions 57 to 61 are based on the following passage. The current emergency in Mexico City that has taken over our lives is nothing. I could ever have imagined for me or my children. We are living in an environmental crisis, an air-pollution emergency of severity. What it really means is that just to breathe here is to play a dangerous game with your health. As parents, what terrorizes us most are reports that children are at higher risk because they breathe more times per minute. What more can we do to protect them and ourselves Our pediatrician’s(儿科医师的) medical recommendation was simple：abandon the city permanently. We are foreigners and we are among the small minority that can afford to leave. We are here because of my husband’s work. We are fascinated by Mexico—its history and rich culture. We know that for us, this is a temporary danger. However, we cannot stand for much longer the fear we feel for our boys. We cannot stop them from breathing. But for millions, there is no choice. Their lives, their jobs, their futures depend on being here. Thousands of Mexicans arrive each day in this city, desperate for economic opportunities. Thousands more are born here each day. Entire families work in the streets and practically live there. It is a familiar sight：as parents hawk goods at stoplights, their children play in the grassy highway dividers, breathing exhaust fumes. I feel guilty complaining about my personal situation；we won’t be here long enough for our children to form the impression that skies are colored only gray. And yet the government cannot do what it must to clad this problem. For any country, especially a developing Third World economy like Mexico’s, the idea of barring from the capital city enough cars, closing enough factories and spending the necessary billions on public transportation is simply not an option. So when things get bad, as in the current emergency, Mexico takes half measures—prohibiting some more cars from circulating, stopping some factories from producing that even its own officials concede aren’t adequate. The word “emergency”implies the unusual. But when daily life itself is an emergency, the concept loses its meaning. It is human nature to try to adapt to that which we cannot change, or to mislead ourselves into believing we can adapt. According to the passage, people in Mexico City are faced with______.

A. serious air pollution
B. economic crisis
C. unemployment
D. natural disaster