Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_91 ( required_os VARCHAR, developer_s_ VARCHAR )

### Question ###
What was the minimum operating system required by Stunlock Studios' game?

### Accurate SQL ###

SELECT required_os FROM table_name_91 WHERE developer_s_ = "stunlock studios"