What type of constraint ensures lines are parallel to the x-axis?

The type of constraint that ensures lines are parallel to the x-axis is the horizontal constraint. In Autodesk Inventor, applying a horizontal constraint to a line defines its orientation so that it remains perfectly aligned parallel to the x-axis, regardless of any modifications made to the geometric relationships within the sketch.

Using a horizontal constraint is particularly useful in creating consistent and organized sketches, as it simplifies the design process by maintaining specific alignments. When you constrain lines this way, it allows for better control over the geometry and aids in achieving a more precise design.

The other options do not achieve the same result. A vertical constraint, for example, would align lines to be parallel to the y-axis, and an orthogonal constraint is designed to create right angles between lines. The diagonal option is not applicable as it does not correspond to a standard constraint type in Autodesk Inventor for controlling line orientation. Therefore, the horizontal constraint is the correct choice for ensuring lines are parallel to the x-axis.