Explanation
According to the AutoCAD for Design and Drafting documents1, the command that should be typed at the command line in order to start creating a line for drawing reference that starts at a defined point and extends to infinity in the designated direction is XLINE2. This command creates a construction line, which is a type of reference line that can help you manage accurate parameters of your drawing2. You can also use point objects as nodes or reference geometry for object snaps and relative offsets3.

Explanation
the mode that should be used if you want the default value of the attribute assigned upon insertion where the attribute value cannot be changed is Constant. This option sets the attribute value as constant and prevents it from being modified during a block insertion or later.
https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/AutoCAD

Explanation
According to the AutoCAD for Design and Drafting documents1, the command that should be typed at the command line in order to start creating a line for drawing reference that starts at a defined point and extends to infinity in the designated direction is XLINE2. This command creates a construction line, which is a type of reference line that can help you manage accurate parameters of your drawing2. You can also use point objects as nodes or reference geometry for object snaps and relative offsets3.

Explanation
The column you should use in the Layer Properties Manager to prevent a layer from being displayed in the active viewport only is "VP Freeze". The VP Freeze column allows you to control the visibility of layers in specific viewports. When you freeze a layer in the VP Freeze column, it is only hidden in the active viewport and remains visible in other viewports. On the other hand, when you freeze a layer with the Freeze column, it becomes hidden in all viewports. Therefore, VP Freeze is the column you should use to hide a layer in a specific viewport only.
https://help.autodesk.com/cloudhelp/2015/ENU/AutoCAD-LT/files/GUID-B297EBD9-D68C-47E1-87CE-1B37

Explanation
* TrueAccording to 1 and 2, UCS is a command that sets the user coordinate system (UCS) which establishes the XY work plane and Z-axis direction for drawing and modeling.
Based on 1, you can use the View option to align the UCS with the current view orientation. This option rotates the UCS so that it matches your current view of a 3D model.
https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/AutoCAD
* Falseccording to 1 and 2, UCS is a command that sets the user coordinate system (UCS) which establishes the XY work plane and Z-axis direction for drawing and modeling.
Based on 1, you can use the World option to set the UCS back to its default orientation. This option resets the UCS so that it matches the WCS (world coordinate system).
https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/AutoCAD
* TrueAccording to 1 and 2, UCS is a command that sets the user coordinate system (UCS) which establishes the XY work plane and Z-axis direction for drawing and modeling.
Based on 1, you can use the Named option to save or restore named UCS definitions. This option allows you to create custom UCSs and switch between them easily.
https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/AutoCAD