How many clients with the last name Alvarado are from Maryland?
The abbreviation of Maryland is 'MD';
SELECT COUNT(T2.client_id) FROM district AS T1 INNER JOIN client AS T2 ON T1.district_id = T2.district_id INNER JOIN state AS T3 ON T1.state_abbrev = T3.StateCode WHERE T2.last = 'Alvarado' AND T2.state = 'MD'