I don't know who inwented_______cell phone,but Ithink it's_______most useful invention.谢谢

I don't know who inwented_______cell phone,but Ithink it's_______most useful invention.谢谢
I don't know who inwented_______cell phone,but Ithink it's_______most useful invention.谢谢

I don't know who inwented_______cell phone,but Ithink it's_______most useful invention.谢谢
the a
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the the

I don't know who invented___the____cell phone,but Ithink it's___a____most useful invention.

the the 后面most useful最高级前加the

I don't know who inwented__the__cell phone,but Ithink it's__the__most useful invention
the 是具体的指出 这个cellphone 是最用用的发明 a= 一个发明 意思