问题补充：
As you know, it is our duty to my younger sisters from being hurt when they are in trouble.
A. prevent
B. save
C. stop
D. protect
答案：
A. prevent
B. save
C. stop
(答案→)D. protect
解析：句意：如你所知，当我们的妹妹处于困境中时保护她们不受伤害是我们的职责。it is our duty to do，it是形式主语，to do sth是真正的主语；save节省，挽救； prevent…from…/ stop…from…阻止某人做某事；protect…from…保护某人/某物不受伤害。这里hurt的逻辑主语是my younger sisters，它们之间是被动关系，故这里用的是being hurt它是动名词的被动语态。根据句意故选D。
