In how many ways can $$12$$ students $$A, B, C, D, E, F, G, H, I, J, K, L$$ line up in a row if students $$A, B$$, $C$ and $D$ 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