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Articles confuse me very much. Please, can anyone tell me which articles should I put in these sentences and why:
__ horse in this photo is beautiful. Is that __ girl or __ boy on its back?
__ castle on that hill is very old. Is that __ bird or __ plane up there (above the castle in the sky)?
In these sentences, I think, "The" article should be in front of 'horse' and 'castle' but which articles should I put in front of the other two words in each sentence?