Ais a statement specifying the condition(s) that must be true before the function is called.
a. precondition
b. postcondition
c. declaration
d. a and b

Precondition

Explanation: Precondition statement is the statement that has the condition for the particular program that has to be correct or true before the execution otherwise the condition can result as undefined. This statement checks that there is no error in the statement  before the function gets called. Similarly post condition is for the checking of the statement after being executed.