CREATE TABLE table_40536 ("Date" CLOB, "Cover model" CLOB, "Centerfold model" CLOB, "Interview subject" CLOB, "20 Questions" CLOB)

When has a Centerfold model of krista kelly?
SELECT "Date" FROM table_40536 WHERE "Centerfold model" = 'krista kelly'
SELECT "Date" FROM "table_40536" WHERE "Centerfold model" = 'krista kelly'