Couldn't both answers be accepted here? The mens' pants are large vs The man's pants are large (as in multiple pairs)
"Bărbaţilor" is the plural, comes from "bărbaţi"
"Barbatului" is the singular, from "bărbat"
So this one translates as "mens' pants".
But without context, i think both should be accepted (talking about the multiple choice exercise). Reported.
If you are you referring to a context in which "Pantalonii bărbaților sunt largi" could be translated as "man's pants" (more pants belonging to a single man), it would be wrong.
Also, "mens' pants" (as in pants designed for men) is usually referred in Romanian as "pantaloni bărbăteşti". For example, in a shop "Aveţi pantaloni bărbăteşti?" - "Have you got mens' pants?"
Feel free to ask me if you have questions, I'm a native speaker and I would gladly answer.
As nunes89 writes, he refers to the multiple choice exercise. Here you can choose between "Pantalonii bărbaților/bărbatului sunt largi". You have no translation, the question is just which word gives a correct sentence. And I agree with nunes that both do but only the first is accepted. I am reporting this.
oh, ok, got it. my bad