Among the white patients, what is the average body height of the patients?
white refers to race = 'white'; average body height = AVG(observations.VALUE WHERE observations.DESCRIPTION = 'Body Height'); body height refers to observations.DESCRIPTION = 'Body Height';
SELECT AVG(T1.VALUE) FROM observations AS T1 INNER JOIN patients AS T2 ON T1.PATIENT = T2.patient WHERE T2.race = 'white' AND T1.DESCRIPTION = 'Body Height'