Query B will return the highest salary in the table without grouping by department. It simply selects the maximum value for the salary column across the entire table.
Query C and D are incorrect because the GROUP BY clause will return the highest salary for each department, not the single highest salary in the entire table.
Query E is incorrect because MAX(MAX(salary)) is not a valid use of aggregate functions and will result in an error.
References:
* Oracle Documentation on Aggregate Functions: Aggregate Functions