This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
In normal dentition, in centric occlusion, opposing contact may be expected at? 
Select and explain. 
A. Buccal slopes of lingual cusps of maxillary posterior teeth., B. Buccal slopes of buccal cusps of maxillary posterior teeth., C. Lingual slopes of lingual cusps of mandibular posterior teeth., D. All of the above.
A: Buccal slopes of lingual cusps of maxillary posterior teeth.
Answer: A: Buccal slopes of lingual cusps of maxillary posterior teeth. 
Explanation: None