一个多项式加上-3x+x-2x2得到x2-1，那么这个多项式为_________。
Mrs Smith is ______ woman. [ ]
A. a eighty-year-old
B. an eighty-year-old
C. an eighty-years-old
D. a eighty-years-old
上颌骨骨折复位后固定时间约为
A．1周B．2周C．3周D．4周E．5周
