What the remote areas need ____ education to children and what the children need ____ good textbooks at the moment.

A．is; are

B．are; is

C．was; were

D．were; was

离子键的强弱主要决定于离子半径和离子电荷值。一般规律是：离子半径越小，电荷值越大，则离子键越强。试分析：①K₂O  ②CaO  ③MgO 的离子键由强到弱的顺序是   

A．③②①

B．③①②

C．②①③

D．①②③