"My sister has many friends."
Translation:Moja siostra ma wiele koleżanek.
We recently resigned from putting "colleague" as the main translation, because it narrows the meaning too much and in a way it can be even considered a false friend.
The problem is that "friend" is very vague from the Polish point of view. It doesn't say much about how close the friendship is. So "koleżanka" is someone whom you (probably) like, but is not among your closest friends (przyjaciele). But it can also be just a colleague from work. Or a schoolmate, or a classmate. Frankly, it's also a rather vague word.
Oh, that's actually a nice surprise that although you only had one letter wrong you still were failed, because this is in fact a mistake.
"wiele" is used with the 'not masculine-personal plural' nouns, so for example "many female friends" is "wiele przyjaciółek".
But for 'masculine-personal plural' nouns ("przyjaciele" imply there's at least one man among them), the right form is "wielu". "Moja siostra ma wielu przyjaciół".