下列各组离子，在溶液中可以大量共存的是（　　）

A．Ag⁺、Ca²⁺、Cl^-、NO₃^-

B．K⁺、NH₄⁺、CO₃^2-、OH^-

C．Na⁺、Cl^-、AlO₂^-、OH^-

D．H⁺、K⁺、CO₃^2-、NO₃^-

______ students should be given more free time is suggested by many experts and welcomed by kids in school．

A．What

B．Why

C．Whether

D．That