CREATE TABLE table_17224 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

Who directed the episode that was viewed by 2.50 million people in the U.S.?
SELECT "Directed by" FROM table_17224 WHERE "U.S. viewers (millions)" = '2.50'
SELECT "Directed by" FROM "table_17224" WHERE "U.S. viewers (millions)" = '2.50'