The correct option is D Sacrum and coccyx
The vertebræ are thirty-three in number, and are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they occupy; there are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal.
The vertebræ in the upper three regions of the column remain distinct throughout life, and are known as true or movable vertebræ; those of the sacral and coccygeal regions, on the other hand, are termed false or fixed vertebræ, because they are united with one another in the adult to form two bones—five forming the upper bone or sacrum, and four the terminal bone or coccyx.