user: ### NOW ANSWER:
Question: What is the 1991 when 1990 is ATP Masters Series?
Columns: ['Tournament', '1984', '1985', '1986', '1987', '1988', '1989', '1990', '1991', '1992', '1993', '1994', '1995', '1996', 'Career SR']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams', 'Grand Slams']
SQL:

assistant: SELECT "1991" FROM "Table" WHERE "1990" = 'ATP Masters Series';