How to add captcha to Google Forms?

It took me some time to search over internet, but can't find it.

Finally I saw a post about how to remove it. WTF? Some people got it and want to remove it, but I don't know how to add it.

Some more investigation and here it is:  Form Settings > General > Collect email addresses

 Enable it. Ok, the email is mandatory. That's it. We can live with that.

Looked at my form. But I didn't see the captcha even it is supposed to be enabled. Oh, now, dead end.

Almost I had right. Not with death, but with the end.
The captcha is at the end of the form. Mine was more than a screen and didn't see it.