"I don't know the crowd."
Translation:Saya tidak kenal kerumunan itu.
Why is "Aku tidak kenal kelompok itu"? incorrect in this multi-choice question. A crowd and a group of people are pretty close in meaning...
I think why it's incorrect is because the word meaning of "the crowd" here is not some specific group of people ("kelompok" specifies a certain number of people), but just many random people being in an area.
Side note: "kelompok" just means group(s). If you want to say a group of people, it should be "sekelompok orang."