The should be used as the relevant article when the noun in the sentence is specific and the only one being referred to as is the case with the boy in this sentence.
2. There is<u> an</u> apple and <u>an</u> orange in the basket.
As both apple and orange begin with vowels or rather have a vowel like sound, the relevant article will be ''an'' because this is the article to be used when referring to vowels.