Most significant will be the availability and price of liquid fuel for transportation.
I don't know if they are solid or liquid fuel.
Two key points discussed in his works are liquid fuels and staging.
He believed that 50 percent efficiency could be achieved with liquid fuel.
It had several advantages over liquid fuels such as gasoline.
Many liquid fuels play a primary role in transportation and the economy.
He might as well have thrown liquid fuel on a fire.
Many of them will expect to travel around by burning liquid fuels.
It's because there is not enough petroleum to meet the demand for liquid fuels now.
We cannot stop the technological development of what is now an alternative to liquid fuels, and perhaps the only one.
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