CREATE TABLE CARS_DATA (edispl INTEGER, Id VARCHAR(255)); CREATE TABLE CAR_NAMES (MakeId VARCHAR(255), Model VARCHAR(255))
What is the average edispl of the cars of model volvo?
    
SQL: SELECT AVG(T2.edispl) FROM CAR_NAMES AS T1 JOIN CARS_DATA AS T2 ON T1.MakeId = T2.Id WHERE T1.Model = 'volvo'