Which residential area in Arecibo county has the highest average house value? Please give its zip_code.
"ARECIBO" is the county; highest average house value refers to Max(avg_house_value)
SELECT T1.zip_code FROM zip_data AS T1 INNER JOIN country AS T2 ON T1.zip_code = T2.zip_code WHERE T2.county = 'ARECIBO' ORDER BY T1.avg_house_value DESC LIMIT 1