$\text{answer should be b)}$$$\text{NOT EXISTS returns TRUE if there are no tuples in the result of nested query , and it returns }$$$\text{FALSE otherwise.}$
$\text{first subquery selects allprojects controlled by department 5, and the second subquery}$
$\text{selects all projects on which particular employee is working and the }$
$\text{difference of the first subquery result EXCEPT the second subquery result is }$
$\text{empty, it means that the employee works on all the projects and is therefore selected.}$