Question: What is the trigger pack on the Colt 602 with the a1 rear sight type?
Schema: create table table_19901_1 (trigger_pack varchar, rear_sight_type varchar, colt_model_no varchar, PRIMARY KEY (trigger_pack))
SQL: select trigger_pack from table_19901_1 where rear_sight_type = "a1" and colt_model_no = "602"