@Thadeo: Without specific context to the contrary, the Hebrew sentence means that the speaker does not want a sour apple (an apple that is sour). To convey that meaning, English requires the indefinite article.
Your answer sounds like an incomplete sentence, such as if "sour apple" is a flavor of pie and the word pie is missing.
Your answer could be correct, though, with the right context, such as if the speaker was replying to the question "What flavor would would you like, apple or sour-apple?" Your translation would be understood to mean that he doesn't want the sour-apple flavor.
@Marva: We have to be careful about absolutes, because there are so many exceptions in language. Your indefinite-article requirement does not apply to uncountable nouns; e.g., "I do not want tea, thanks."
Also, although not related to this sentence exercise, your definite-article requirement does not always apply to proper nouns. So, while you may say "I do not want the Datsun", you can also say "I do not want Alfred E. Neuman as umpire."
2020-02-01 rich739183, edited 2020-11-11
Pe (פ) makes both an f and p sound, depending on where it is in the word and other factors.
Think about פ as similar to c in English...sometimes it’s s as in ice, sometimes it’s a k sound as in miracle, and sometimes an Italian rule makes it a ch sound, as in cello.
At the beginning of a word, פ will always be pronounced as p.