CREATE TABLE table_48274 ("Tournament" TEXT, "1984" TEXT, "1985" TEXT, "1986" TEXT, "1987" TEXT, "1988" TEXT, "1989" TEXT, "1990" TEXT, "1991" TEXT, "1992" TEXT, "1993" TEXT, "1994" TEXT, "1995" TEXT, "1996" TEXT, "Career SR" TEXT)

What is the 1991 when 1990 is ATP Masters Series?
SELECT "1991" FROM table_48274 WHERE "1990" = 'atp masters series'
SELECT "1991" FROM "table_48274" WHERE "1990" = 'atp masters series'