A face-centred cubic (FCC) unit cell and a body-centred tetragonal (BCT) unit cell are fundamentally different crystal systems with distinct lattice parameters and symmetry properties.
The claim states a basic, universally accepted crystallographic fact: face-centred cubic and body-centred tetragonal are distinct unit cell types defined by different Bravais lattices. According to the instructions, statements that are trivially true by definition or direct everyday/textbook observation are classified as COMMON_KNOWLEDGE and do not require citations, even though background papers discuss FCC and BCT structures.