He turned ________ ten years ago but later he became ________.   [ ]

A. a teacher; a doctor    

B. teacher; doctor  

C. teacher; a doctor    

D. a teacher; doctor

下列离子组能在酸性溶液中大量共存的是  

A．K^＋、Mg²⁺、Cl^－、SO₃^2－

B．Cu²⁺、K^＋、Cl^－、SO₄^2－

C．NH₄^＋、Na^＋、CO₃^2－、OH^－

D．Ca²⁺、HSO₃^－、K^＋、SO₄^2－