Explanation:

- Option 1: Unless

- This means "except if" or "on the condition that."

- It implies a condition that has not been met for another action to happen.

- Not suitable here as it doesn't fit the context of a conclusion or sequence.

- Option 2: While

- Indicates two actions happening simultaneously.

- Suggests that something occurred during the time another action was ongoing.

- Doesn't fit here because the ovation happens after the play ends.

- Option 3: Since

- Often used to indicate a reason or cause for something, or a time lapse.

- Doesn't match the timing or causation implied in the sentence.

- Option 4: When

- Used to indicate a specific time or event something happened.

- Fits perfectly as it denotes the timing of the ovation immediately after the play's conclusion.

* The most appropriate option is Option 4 - When.*