[单项选择]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 unprecedented 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 job A. serious air-pollution B. economic crisis C. unemployment D. natural disaster