CREATE TABLE table_18173 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" FLOAT, "Results" CLOB, "Candidates" CLOB)

What district is bill thomas from?
SELECT "District" FROM table_18173 WHERE "Incumbent" = 'Bill Thomas'
SELECT "District" FROM "table_18173" WHERE "Incumbent" = 'Bill Thomas'