My brother was making a-lot of noise _____ I was doing my homework. [ ]

A. but

B. and

C. while

下列能在水中大量共存的一组离子是（　　）

A．K⁺、OH^-、NO₃^-、H⁺

B．K⁺、Ag⁺、NO₃^-、Cl^-

C．Ba²⁺、H⁺、Cl^-、SO₄^2-

D．Na⁺、Ba²⁺、OH^-、NO₃^-