Extracted text: In the database relation R(a, b, d, e, f) attribute b and d are dependent only on a; e only on d; and f only on d. Which of these sets of relations is equivalent to R in third normał form (3NF), if key attributes are underlined? A RI(a, b), R2(d, e,f), R3(a, d). B RI(a, b, d), R2(d, e), R3(e. f). C RI(a, b, d), R2(d, e), R3(e,f) D RI(a, b, d), R2(d, e,f).