Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:

Convert text to sql: Find the last name of students who is either female (sex is F) and living in the city of code BAL or male (sex is M) and in age of below 20. | student : stuid , lname , fname , age , sex , major , advisor , city_code | dorm : dormid , dorm_name , student_capacity , gender | dorm_amenity : amenid , amenity_name | has_amenity : dormid , amenid | lives_in : stuid , dormid , room_number | has_amenity.amenid = dorm_amenity.amenid | has_amenity.dormid = dorm.dormid | lives_in.dormid = dorm.dormid | lives_in.stuid = student.stuid | 

### Response:

select _ from _ where _ union select _ from _ where _ | select lname from student where sex = 'F' and city_code = 'BAL' union select lname from student where sex = 'M' and age < 20