In France it is the__________ to shake hands with people in the office every morning.

A．habit

B．behavior

C．custom

D．act

能在水溶液中大量共存的一组离子是（　　）

A．H⁺、Fe³⁺、I^-、SO₄^2-

B．Al³⁺、Mg²⁺、CO₃^2-、Cl^-

C．K⁺、Ag⁺、Ca²⁺、NO₃^-

D．NH₄⁺、Na⁺、OH^-、MnO₄^-