weak在句中可用作表语,也可用作定语。用作定语时,其后可接具体名词或抽象名词,作表语时,其后可接介词短语、动词不定式或that从句。
例句：
①用作形容词 (adj.)
用作定语: ～+ n.
She spoke in a weak voice.
她有气无力地说话。
②用作表语: S+be+～
Her pulse is weak; she must be very ill.
她的脉搏微弱,必定病得很厉害。
③S+be+～+ prep .-phrase
She was weak from a long illness.
她因长期生病而十分虚弱。
④S+be+too ～+to- v
The flu victim was too weak to walk.
这位流感病人虚弱得连路都走不动。
⑤S+be+～+that-clause
The teacher's so weak that the children do what they like.
这老师太软弱了,孩子们因此可以为所欲为。
短语：
weak answer 缺乏说服力的回答
weak character 优柔寡断的性格
weak coffee 淡咖啡
weak constitution 虚弱的体质
weak defence 不牢固的防御工作
