A relation R(A, B, C, D) has the functional dependencies F = {AB -> C, C -> D, D -> A}. What is the highest normal form satisfied by R?

First, find candidate keys. The closures of candidate keys include {AB} and {BD}. Since C -> D and D -> A, attribute C determines D, and D determines A, making C and D prime or non-prime depending on the key analysis. Specifically, for C -> D and D -> A, neither C nor D is a superkey. Therefore, BCNF is violated because the left-hand sides (C and D) are not superkeys. However, 3NF is satisfied because for every non-trivial functional dependency X -> Y, either X is a superkey or Y is a prime attribute.