What we must do with fossil fuels? It's vain (7)
I believe the answer is:
useless
'vain' is the definition.
(I've seen this before)
'what we must do with fossil fuels? it's' is the wordplay.
I cannot quite understand how this works, but
'we' could be 'us' and 'us' is found within the answer.
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is found in the answer.
The remaining letters 'els' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for useless that I've seen before include "Ineffective" , "Counterproductive" , "Unemployable" , "Not practical or constructive" , "Having no benefical function" .)