1.Those especially at risk include persons who inject themselves with drugs and those who received blood or blood products before nineteen ninety.

at risk有危险

例句：The disease is spreading, and all children under five are at risk.
      这疾病在蔓延, 五岁以下的小孩都有危险。

2.Doctors say the best way to prevent hepatitis D is to get vaccine that protects against hepatitis B. Doctors can treat some cases of hepatitis B, C and D.

动词不定式做表语

不定式位于系动词如be之后用来说明主语的身份、特征、属性或状态

Her ambition was to be a star. 她的志向是当明星。

My task is to take care of my little brother. 我的任务是照顾弟弟。

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