Final answer:
Above the apices of maxillary teeth lies the floor of the nasal cavity. The maxillary bone forms this floor along with the hard palate which separates the oral and nasal cavities.
Step-by-step explanation:
The structure that appears above the apices of the maxillary teeth is the floor of the nasal cavity. The maxillary bone, or maxilla, helps form the upper jaw and the hard palate, the latter being part of the floor of the nasal cavity and the roof of the mouth. The maxilla contains the alveolar process, where each tooth is anchored into a socket called an alveolus. The hard palate is the bony plate that forms part of the floor of the nasal cavity and separates the oral and nasal cavities, whereas the soft palate is located posteriorly and is primarily made of skeletal muscle. Therefore, the correct answer is 4) Floor of the nasal cavity.