This is an old question that is no longer in use.
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Which fuel contributes the least to the greenhouse effect?
“Biofuels [...] have the benefit of not contributing to the greenhouse effect.” (Driving Licence Book, 19th Edition, page 227)
Natural gas is not as good as it sounds. It is, just like petrol and diesel, a fossil fuel.
There is also a driving licence book online (2023).
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