When thomas löfkvist is the  young rider classification and alessandro petacchi is the points classification who are the general classifications?
create table table_18733814_2 (general_classification varchar, points_classification varchar, young_rider_classification varchar, PRIMARY KEY (general_classification))
select general_classification from table_18733814_2 where points_classification = "alessandro petacchi" and young_rider_classification = "thomas löfkvist"