脊髓下端上移至第1腰椎的年龄是()
A.6个月
B.1岁
C.2岁
D.4岁
E.3岁
参考答案:D
Oil prices have risen by32 percent since the start of the year,_____a record US $57.65 a barrel on April 4.
A.have reached
B.reaching
C.to reach
D.to be reaching
皇冠上有一颗透明的红宝石,不拆下来如何鉴定它是红宝石还是红色尖晶石:().
A.测折射率
B.测比重
C.观察二色性
D.用偏光仪测非均质体还是均质体