"Ils regardent pendant qu'elle écrit ses lettres."
Translation:They watch while she writes her letters.
If you're asking about the audio, the singular and plural sound the same. "Il regarde pendant qu'elle écrit ses lettres" was accepted for me.
It has now been added to the list of homophones and will be accepted as soon as staff processes it.
Possessive adjectives (son/sa/ses) may be either "his" or "her" grammatically, but in reality they will be understood as a reflection of the subject of the sentence, or in this case, the phrase, i.e., "elle". So the expression "elle écrit ses lettres" would be understood as "she writes her letters". If you want to avoid confusion, you may say "elle écrit ses lettres à lui" = she writes his letters.
In the audio, is there a way to tell the difference between ces and ses? '... while she writes the letters' sounded logical in English.
Apparently not; DL accepted "Il regarde pendant qu'elle écrit ces lettres" just now.
I wrote "the look while she writes her letters" and was marked wrong. Should that not be accepted?
There is no "the look". It is "they look" (ils regardent). Yes, it is only one letter off but it is wrong. The question for you is what do you think it means to say "the look while she writes her letters"? It is rather meaningless. So how can you translate from one language to another without knowing what it means or if what you have written produces a correct, meaningful statement?
I feel like the question they were meaning to ask is why "look" was not able to be used as the verb in the sentence -- why "regardent" had to be translated as "watch" to be marked correct.