To answer this question, the user needs to have knowledge of different types of arguments in programming.
a) VARCHER2: This is not a type of argument. It is a data type used to store character strings in Oracle database.
b) BOOLEAN: This is not a type of argument that passes a value from a calling environment.
c) OUT: This type of argument passes a value to the calling environment. It is used when a function or procedure needs to return more than one value.
d) IN: This type of argument passes a value from the calling environment to the function or procedure. It is used when a function or procedure needs to receive values from the calling environment.
Optimistic locking is a technique used to prevent data conflicts in a multi-user environment. It involves checking for conflicts only at the time of update, that is, when a user tries to modify a piece of data that may have already been modified by another user. If a conflict is detected, the optimistic locking mechanism rolls back the transaction and the user has to redo their work. Therefore, option A is correct. Option B is incorrect because it contradicts the explanation given above.