单项选择题
In limited test B for arsenic,which of the following should be ready according to BP(1993 edition)（）
A．Sodium hydroxide B．arsenic standard solution C．iodide chloride D．Wagner reagent E．Sand bath
A．持续振摇 B．间续振摇 C．猛烈振播 D．轻轻振摇 E．边振摇边搅拌