_____ of their bad habits, the boys switched from being dependent on their parents to _____ for others
A.Having rid; sacrificingB.To rid; sacrificeC.Rid; sacrificingD.Having been rid; sacrifice在线课程A
本题考查非谓语动词。句意：通过摆脱坏习惯后，男孩们从依赖父母的人变成了可以为他人牺牲的人。the boys是rid的执行者，要用现在分词的主动形式，排除C和D。switch from…to... （从……转向……）中to是介词，后跟doing。