user: Question: What is the episode number in the series for "Graduation" that was directed by Don Corvan?
Columns: ['Ep.', 'Season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Prod. Code']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [52.0, 1.0, '"Initiation"', 'Michael Zinberg', 'Frank Dungan & Jeff Stein & Tony Sheehan', 'October 30, 1987', '5M03']
SQL:

assistant: SELECT "Ep." FROM "Table" WHERE "Directed by" = 'Don Corvan' AND "Title" = '"Graduation"';