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
The internal wall perpendicular to the long axis of the tooth in a Class II amalgam preparation is ______. 
Select and explain. 
A. Pulpal floor, B. Axial wall, C. Gingival floor, D. Enamel wall
A: Pulpal floor
Answer: A: Pulpal floor 
Explanation: There are two types of internal walls. The axial wall is an internal wall that is oriented parallel to the long axis of the tooth.
The pulpal wall is an internal wall that is oriented perpendicular to the long axis of the tooth and is located occlusal to the pulp. This internal wall may also be referred to as the pulpal floor.
The external wall that is approximately horizontal (i.e., perpendicular to the occlusal forces that are directed occlusogingivally and generally parallel to the long axis of the tooth crown may also be referred to as a preparation floor (e.g., a gingival floor).
The enamel wall is that portion of a prepared external wall consisting of enamel.

Reference: Sturdevant operative dentistry. 7th edition pg no 123