"They don't need their socks."
Translation:הם לא צריכים את הגרביים שלהם.
In this sentence, the multiple choice exercise marks the option "הם לא צריכים את הגרביים שלהן" as incorrect, although it is technically correct (שלהן is also "their"), even if it would mean that they do not need someone else's socks, the socks of some women or girls, not their own. But it is still translated as "They don't need their socks", so it should be a correct option.
It cannot be reported directly, there's no option "My answer should be accepted" in the multiple choice exercise. So I'm writing here. I've already reported a similar mistake in comments once, and the team fixed it.