双曲线x2－ay2＝1的焦点坐标是           （   ）

A：(, 0) , (－, 0)

B：(, 0), (－, 0)

C：（－, 0）,（, 0）

D：(－, 0), (9 and thought it was raining. When people are really   10  , nothing will stop them from falling asleep--no matter where they are.