One thing, Klaatu. Suppose this group should reject your proposals.

8 seconds sound clip from the The Day the Earth Stood Still (1954) classic radio play.

You can hear this line at 00:26:00 in the radio play.

Quote context

[...]

- Must I take drastic action in order to get a hearing?

- What sort of action do you mean?

- Violent action?

- Perhaps leveling the island of Manhattan... or toppling the Rock of Gibraltar into the sea? Well?

- Would you, for example, be willing to meet with a group of scientists I am calling together? We're having our first meeting tonight.

- Perhaps you could explain your mission to them, and they in turn could present it to their various peoples.

- That is what I came to see you about.

- One thing, Klaatu. Suppose this group should reject your proposals.

- What is the alternative?

- There is no alternative, Professor. In such a case, the planet Earth would have to be eliminated.

- Such power exists?

- I assure you, such power exists.

- The scientists who are attending these meetings have come here from all over the world.

- This power you speak of... They must be made to realize that it exists.

[...]