An attacker is launching an attack against an input field in a form that is used to retrieve restricted information that is filtered dependent upon the privileges of the logged in user. This attacker

Authentication bypass via SQL injection targets a login form where credentials are validated, not a data-retrieval field that filters results by privilege level.

While 'or 1=1' does create a true condition, choice B is considered incomplete because it only references the mechanism and not the full attacker goal of extracting all restricted rows regardless of the logged-in user's privilege.

A UNION-based injection requires the UNION keyword in the payload to append a second SELECT statement; the string ' or 1=1;-- contains no UNION clause.

The single quote closes the existing string literal in the SQL query, and 'or 1=1' appends an always-true condition that overrides the privilege filter logic. The double-hyphen (--) comments out the remainder of the original query, preventing syntax errors. The combined effect causes the database to ignore user privilege constraints and return every row in the table to the attacker.