Consider the set of relations shown below.

Students $($Roll$\_$number, Name, Date$\_$of$\_$birth$)$

$$ Courses $($Course$\_$number, Course$\_$name, Instructor$)$ Grades $($Roll number, Course$\_$number, Grade$)$

Now consider the query SELECT DISTINCT Name FROM Students, Courses, Grades

WHERE Students Roll$\_$number Grades Roll$\_$number

AND Courses Instructor 'Korth'

AND Courses Course$\_$number Grades.Course$\_$number

AND Grades.grade $=\text{'}$A$\text{'}$

Which of the following sets is computed by the above

Select one:

a$.$ Names of students who have got an A grade in all courses

b$.$ Names of students who have got an A grade in all courses taught by Korth

c$.$ Names of students who have got an A grade in at least one course

d$.$ Names of students who have got an A grade in at least one of the courses taught by Korth