Go to Preferences -> Keyboard. At the bottom, turn on "All controls" under "Full Keyboard Access".
The alternate option will be highlighted with a blue ring. Hitting space will activate this. If there are multiple options, hitting tab will alternate between them.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…