Read the statement and the instructions that follow it, and then make any notes that will help you plan your response. Write your response on a separate sheet of paper. If possible, type your essay on a word processor.
Since unhealthy people increase health-care costs for all of society, society should impose greater penalties on those people who voluntarily indulge in unhealthy activities, such as smoking, excessive drinking, or overeating.
Discuss the extent to which you agree or disagree with the opinion stated above. Support your views with reasons and/or examples from your own experiences, observations, or reading.

书中给出的自然对流时计算αc的三个公式中，系数分别为2.0，2.5，1.3，试说明系数不同的原因。