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_76 ( year_opened VARCHAR, students VARCHAR, size VARCHAR )

### Question ###
What year was the school opened that has a size of 10 acres and students of na?

### Accurate SQL ###

SELECT year_opened FROM table_name_76 WHERE students = "na" AND size = "10 acres"