Respond nervously regarding carbon fuel (6)
I believe the answer is:
recoil
'respond nervously' is the definition.
I can't judge whether this defines the answer.
'regarding carbon fuel' is the wordplay.
'regarding' becomes 're' ('re' means regarding or about).
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'fuel' becomes 'oil' (oil is a type of fuel).
're'+'c'+'oil'='RECOIL'
Can you help me to learn more?
(Other definitions for recoil that I've seen before include "Jump back" , "Feel disgust" , "(As a firearm) spring back" , "withdraw" , "Quail is here!" .)