下列各组离子，在溶液中能大量共存、加入NaOH溶液后加热既有气体放出又有沉淀生成的一组是 [ ]

A．Ba²⁺、NO₃^-、NH₄⁺、Cl^-

B．Ca²⁺、HCO₃^-、NH₄⁺、AlO₂^-

C．K⁺、Ba²⁺、Cl^-、HSO₃^-

D．Mg²⁺、NH₄⁺、SO₄^2-、K⁺

      ---What are you busy with ?

--- We are carrying out a research ____ the causes of cancer.

A．into

B．onto

C．to

D．in