颈段前屈角度是
A．45°B．60°C．50°D．80°E．20°
参考答案：A
The first month of the year is ________.[ ]
A. January
B. February
C. March
D. December
国民生产净值又叫( )。
A．GDP
B．GNP
C．NNP
D．PDI
