In how many ways can $$6$$ students $$A, B, C, D, E, F$$ line up in a row if students $$A$$ and $$B$$ are always next to each other? 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Permutations->Basic Operations of Permutations Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations