CREATE TABLE table_60954 ("Event" CLOB, "Time" CLOB, "Nationality" CLOB, "Date" CLOB, "Meet" CLOB, "Location" CLOB)

What is Date, when Meet is 'World Championships', when Nationality is 'United States', and when Time is '1:46.68'?
SELECT "Date" FROM table_60954 WHERE "Meet" = 'world championships' AND "Nationality" = 'united states' AND "Time" = '1:46.68'
SELECT "Date" FROM "table_60954" WHERE "Meet" = 'world championships' AND "Nationality" = 'united states' AND "Time" = '1:46.68'