Among the car models introduced in the market in 1970, how many of them have the USA as their origin country?
introduced in the market in 1970 refers to model_year = 1970; have the USA as origin country refers to country = 'USA'
SELECT COUNT(*) FROM production AS T1 INNER JOIN country AS T2 ON T1.country = T2.origin WHERE T1.model_year = 1970 AND T2.country = 'USA'
database name:db_id cars
country table country Cols: origin dtype integer, country dtype text, 
price table price Cols: ID dtype integer, price dtype real, 
data table data Cols: ID dtype integer, mileage per gallon dtype real, number of cylinders dtype integer, displacement dtype real, horse power dtype integer, weight dtype integer, acceleration dtype real, model dtype integer, car name dtype text, 
production table production Cols: ID dtype integer, model year dtype integer, country dtype integer, 
