甲、乙两地某病粗死亡率相等，经过年龄标化后，甲地标化死亡率高于乙地，原因可能是（）。

A．甲地老年人比重高于乙地

B．甲地和乙地人群的年龄构成不同所致

C．与年龄构成无关

D．甲地诊断的准确率高

E．甲地女性人口数高于乙地

Mr. Smith spoke slowly and clearly to _____ all of us students could follow him.

A．test

B．be sure

C．examine

D．make sure