Table schema:
CREATE TABLE CARS_DATA (edispl INTEGER, Id VARCHAR); CREATE TABLE CAR_NAMES (MakeId VARCHAR, Model VARCHAR)

Question: 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'