_____ of their bad habits, the boys switched 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

答案及解析： 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。