The school rule states that no child shall be, unless        by an adult, allowed out of the school during the day.

A．was accompanied

B．accompanying

C．accompanied

D．being accompanied

对由X、Y元素形成的化合物X₂Y₂的叙述正确的是（    ）

A．若是离子化合物，则阳阴离子个数比肯定不等于1：1

B．若由分子构成且有Y-Y键，则肯定是非极性分子

C．若溶于水时有X-Y键的断裂，则肯定是强电解质

D．若X、Y原子间的共价键键能大，则熔、沸点肯定高