APPLYING SUBSTITUTION VARIABLES:

a) PL/SQL is not a stand alone programming language, it only exists as a tool within the Oracle programming environment.
b) Because of the alone mentioned standard it does not really have capabilities to accept input from user.
c) For accepting the inputs the substitutions variables can be used, which can be either '&' or'&&'.
d) Substitutions variables cannot be used to output the values.
e) The substitutions of the value is actually done by the SQL*PLUS environment, before the PL/SQL block is sent to the database.