Question

look at the diagram above. what is part of the arch’s anatomy is (a) labeling?
a. impost
c. keystone
b. springing line
d. voussoir

Explanation:

To determine the part labeled A in the arch's anatomy, we analyze each option:

• Impost (a): Supports the springing line, not the top central stone.
• Springing line (b): The line where the arch "springs" from the impost, not the top stone.
• Keystone (c): The central, top stone of an arch that locks the voussoirs (other stones) in place. In the diagram, A is the top - central (orange) stone, matching the keystone’s role.
• Voussoir (d): A wedge - shaped stone in the arch (like the blue ones, labeled B), not the central top stone.

Answer:

c. keystone