Where is the Option key on non standard keyboard?

[Willabong]

"Shut down your Mac, then turn it on and immediately press and hold these four keys together: Option, Command, P, and R."

That is the information I have been given, but I have no idea which key is the Option key as this is not named on my keyboard?
I am trying to reset this iMac so I can give it to a charity shop. Any help appreciated?

 

[chscag]

The "Option" key may also be marked as "alt". If you're using a non standard keyboard or a Windows keyboard, press the "alt" key for "option".

 

[Willabong]

Thanks chscag, I thought it was alt, but I had to make sure first!