For example, three people, A, B and C, I want to choose two of them.

If it is arranged, the general topic or text description will emphasize the order. For example, I take A first, then B and B first, and then A is two different arrangements, because there are objective differences: people are different. The title also emphasizes (subjective) order. For example, among the two candidates, I think A has more advantages than B, so A is the first candidate and A is the second candidate, which is different.

If it is a combination, then take A first, then B first, then B first, then A is also the same combination, because although there are differences between objective people here, there is no emphasis on the order. Whoever takes it first will be the last one. In other words, subjectively speaking, they have no order and no sense of superiority.