单项选择题
A．the greenhouse effect B．the burning of fossil fuels C．the potential effect of air pollution D．the likelihood of a new ice age
A．may be inhabited by attractive Martians B．may have some vegetable life C．can have no life at all D．may have both vegetable and animal life
A．dealing with the academic affairs of the university B．ensuring that the students observe university regulations C．evaluating students’ performance by bringing them before a court D．keeping up the students’ enthusiasm for social activities