One of the main advantages of a graphite-furnace atomizer is that（）

A.It requires only very small quantities of a sample

B.It requires metal.ions in aqueous solution

C.It does not produce background emission like a flame

D.It does not get hot like a flame

根据钢结构设计规范（GB50017-2003），承载能力极限状态包括（）

A.构件和连接的强度破坏而不适于继续承载

B.构件和连接的疲劳破坏和因过度变形而不适于继续承载

C.结构和构件丧失稳定

D.结构转变为机动体系和结构倾覆