Related Clues:

• Take countermeasures
• Answer an invitation
• Echo, e.g.
• E-mail option
• Flinch, say
• Change chemically
• Push back, perhaps
• Come back
• It's much requested
• 'Is that your final ___?'
• Don't just sit there
• Jerk one's knee, e.g.
• Don't just stand there
• Strike back
• Answer