In 3D solid modeling (e.g., AutoCAD), to create a single unified solid from two or more separate solid bodies, the drafter must first position the solids correctly and then apply which operation?

Introduction / Context:
When working with solid modeling, designers often build complex parts by combining simpler primitives (box, cylinder, wedge). After positioning these bodies, you typically need a Boolean operation to merge them into one watertight solid for mass properties, filleting across seams, and clean downstream manufacturing data.

Given Data / Assumptions:

• Two or more separate solid bodies are already modeled and positioned with correct alignment.
• The goal is to convert multiple solids into a single, unified solid.
• Standard AutoCAD-style solid editing tools are available.

Concept / Approach:
Solid modeling uses three core Boolean operations: Union, Subtract, and Intersect. Union combines volumes into one contiguous solid, removing internal faces at the junctions. Subtract removes one volume from another. Intersect keeps only overlapping volume. For merging, Union is the correct choice.

Step-by-Step Solution:

Verification / Alternative check:
Use MASSPROP to confirm a single volume and check that edges across former boundaries fillet or chamfer continuously—an indication of a true union.

Why Other Options Are Wrong:

• use the Join command: Join applies to curves/surfaces, not combining separate 3D solids.
• use the Add Parts tool: Not a standard AutoCAD solids command; misleading.
• none of the above: Incorrect because Union is exactly the required tool.

Common Pitfalls:
Attempting Union on non-solids (e.g., surfaces) or touching solids that only meet at an edge may fail. Ensure bodies overlap or meet with faces for reliable results.

Final Answer:
use Union to join them