Below is an instruction that describes a task. Write a response that appropriately completes the request.

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

### Inputs:
table_name: table, columns: ['Editor', 'Site', 'Style, clone of', 'Cost ( US$ )', 'Open source', 'Activity']

### Response:
SELECT Open source FROM table WHERE Cost ( US$ ) = free AND Activity = some AND Editor = markitup