be unfastened
表示状态，用be动词+过去分词作表语。
The belt was unfastened.
腰带被解开了。
解开（尤指衣服或带子）；松开
先理解核心含义，再看它在真实句子里的用法。
解开（尤指衣服或带子）；松开
to cause something to become undone; to become undone or untied
一般现在时
I unfasten my seatbelt.
我解开安全带。
She unfastened her seatbelt as soon as the plane landed.
飞机一着陆，她就解开了安全带。
用法提示：这里“unfastened”是动词过去式，表示解开安全带的动作。
He unfastened the buttons on his shirt because it was too hot.
因为太热了，他解开了衬衫的扣子。
用法提示：“unfastened”是动词过去式，表示解开纽扣的动作。
The child unfastened the straps of her backpack to take out a book.
孩子解开了背包的带子，拿出一本书。
用法提示：“unfastened”是动词过去式，表示解开背包带子的动作。
表示状态，用be动词+过去分词作表语。
The belt was unfastened.
腰带被解开了。
过去式形式为 unfastened。
She unfastened her necklace.
她解开了项链。
unfastened 作定语修饰名词。
He noticed the unfastened button.
他注意到了那颗未扣好的纽扣。
grammar · medium
易错句子Please unfastened your coat.
正确表达Please unfasten your coat.
错误使用了过去分词 unfastened 作为祈使句的动词原形，应该用动词原形 unfasten。
grammar · medium
易错句子The window is unfastening.
正确表达The window is unfastened.
描述窗户的状态（未关紧）应使用过去分词 unfastened 作形容词，而不是现在分词 unfastening，后者表示正在进行的动作。
untied 专指鞋带、绳结等系物被解开；unfastened 范围更广，可指衣服、带子、锁扣等任何固定物被松开。
unbuttoned 仅指纽扣被解开；unfastened 可泛指任何闭合方式（如纽扣、拉链、钩环等）被松开。
unlocked 专指锁未被锁上；unfastened 通常不用于锁具，而是用于衣物、带子等可系紧之物。
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