Answer the following regarding free-body diagrams (FBDs):
a. (i) Define a free-body diagram.
b. (ii) State any four common external forces that may appear in a free-body diagram and mention one physical situation corresponding to each force.
c. (iii) List the standard steps that should be followed while constructing a correct free-body diagram of a mechanical system.
d. (iv) For a block placed on a rough horizontal table and at rest, name all the external forces acting on the block.