このボタンを押す___、切符が出ます。
Q. Which conditional fits a machine's automatic result?
Translation
When you press this button, a ticket comes out.
Explanation
と expresses an automatic, invariable result — perfect for machines and natural laws: 押すと出ます. たら and ば are possible in some contexts, but for 'whenever X, Y always happens' と is the most natural.