腰椎间盘突出症发病率最低的年龄段是（）
A.20～29岁
B.30～39岁
C.40～49岁
D.50～59岁
E.60岁以上
参考答案：E
读问题，再回答。
1. Which season do you like best?_________________________________
2. When's your birthday?________________________________________
3. What time is it?_____________________________________________
4. When do you eat breakfast?___________________________________
5. What season is it now?_______________________________________
在通常条件下，下列各组物质的性质排列正确的是[ ]
A．热稳定性：HF﹥H2O﹥NH3
B．水溶性：HCl﹥SO2﹥NH3
C．沸点：乙烷﹥戊烷﹥丁烷
D．酸性：H2SO4﹥H3PO4﹥HClO4
