I live in a city which doesn't have any seacoast.

To live in a city “where” doesn’t have any coast by the sea

“Where” is wrong to use here ?

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Yes-- or other parts are wrong. These are OK:

I live in a city which doesn’t have any seacoast.
I live in a city where there is no seacoast.

why to use “where” is wrong in my sentence ?

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‘Where’ is an adverb and cannot be the subject of the verb, ‘doesn’t have’.
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Hi Volcano,

Please read why is a meaningful message title important? and let me know what you think.
Many thanks,
Torsten[YSaerTTEW443543]

TOEIC listening, talks: Update on current marketing/advertising campaign of sports equipment company[YSaerTTEW443543]

Thanks,I will consider the next time