CREATE TABLE table_44750 ("Date" TEXT, "Series" TEXT, "Circuit" TEXT, "City / State" TEXT, "Winner" TEXT, "Team" TEXT)

What is Circuit, when Series is ASTC Round 4?
SELECT "Circuit" FROM table_44750 WHERE "Series" = 'astc round 4'
SELECT "Circuit" FROM "table_44750" WHERE "Series" = 'astc round 4'