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_48 ( open_source VARCHAR, editor VARCHAR, cost___us$__ VARCHAR, activity VARCHAR )

### Question ###
Which source has a Cost free, and an Activity of some, and an Editor of markitup?

### Accurate SQL ###

SELECT open_source FROM table_name_48 WHERE cost___us$__ = "free" AND activity = "some" AND editor = "markitup"