________of their bad habits, the boys changed from being dependent on their parents to ________for others.A. Having rid; sacrificing B. To rid; sacrifice C. Rid; sacrificing D. Having been rid; sacrifice 答案:【答案】C【解析】考查非谓语动词。句意:那些男孩通过摆脱坏习惯而变到从依赖父母转向可以为他人牺牲。from…to为固定搭配,且该搭配中的from和to都是介词,故其后的动词该使用现在分词形式,因此B、D选项直接排除。be rid of意为摆脱;革除,因为孩子与革除之间是动宾关系,故直接使用动词的过化学符号“2H”中“2”表示( ) A. 两个氢原子 B.氢的化合价为+2价 C. 两个氢元素 D.氢气分子由2个氢原子构成