Why is this the right answer? Please really motivate so it's understandable, thanks.

STUDENT StudentID StName 1 Pericles 2 Alexander 3 Ptolemy 4 Euclid Pythagoras Aristotle Supervisor ID Project Grade 1 5 1 5 2 NULL 3 4 2 3 2 4 SUPERVISOR SupervisorID SupName 1 Thor 2 Marcus 3 Magnus 4 Caesar Question 13 Which of the following statanents will retum (1) the average project grade of students per supervisor (ii) together with the supervisor's name? Select SupName, Avg (ProjectGrade) From SUPERVISOR, STUDENT Where STUDENT. Supervisor ID-SUPERVISOR.SupervisorID; B Select SupName, Avg (ProjectGrade) From SUPERVISOR, STUDENT Where STUDENT. Supervisor ID-SUPERVISOR.SupervisorID Group By SUPERVISOR.SupervisorID; Select SupName, Avg(ProjectGrade) From SUPERVISOR, STUDENT Where STUDENT. SupervisorID=SUPERVISOR. SupervisorID Group By STUDENT. Student ID; Select SupName, Avg(ProjectGrade) From SUPERVISOR Left Join STUDENT On STUDENT. Supervisor ID-SUPERVISOR.SupervisorID Group By STUDENT. SupervisorID; AnswerB