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[det] + dog
dog 是可数名词，前面通常需要限定词。
I saw a dog in the park.
我在公园里看到一只狗。
狗；犬
先理解核心含义，再看它在真实句子里的用法。
狗；犬
a domesticated carnivorous mammal of the genus Canis, kept as a pet or for work
I saw a dog in the park.
我在公园里看到一只狗。
犬科动物,由灰狼驯化,自史前被人类驯养,品种繁多。
a member of the genus Canis (probably descended from the common wolf) that has been domesticated by man since prehistoric times; occurs in many breeds
丑陋无趣的女人
a dull unattractive unpleasant girl or woman
对男人的非正式称呼
informal term for a man
My dog loves to play in the park.
我的狗喜欢在公园里玩。
AI contextual example
She takes her dog for a walk every morning.
她每天早上带她的狗去散步。
AI contextual example
The dog barked loudly when the doorbell rang.
门铃响时，那只狗大声叫了起来。
AI contextual example
the dog barked all night
那只狗叫了一整夜
WordNet
dog 是可数名词，前面通常需要限定词。
I saw a dog in the park.
我在公园里看到一只狗。
dog 常与其他名词构成复合词。
She bought some dog food.
她买了一些狗粮。
He followed me around like a dog.
他像狗一样跟着我。
Not this
I have dog.
Use this
I have a dog.
可数名词单数形式前必须加冠词（a/an/the），中文“狗”可泛指，但英语中单数可数名词不能单独使用。
Not this
Dog is animal.
Use this
A dog is an animal. 或 Dogs are animals.
表示类别时，可数名词要么用复数，要么用单数加冠词；不能直接用单数光杆名词。