(b) in Maginot's defence, junior french planners may well have imagined a Blitzkrieg, and rightfully discarded it, assuming the germans wouldn't have an energy source. A coal-based army doesn't move quickly.
The french were to learn that a synfuel-based[1] army can blitz. The germans, on the other hand, had to blitz: after failing[2] to reach Grozny and Baku to replenish energy stocks they were put on the defensive.
Crude Rules Everything Around Me
[1] https://en.wikipedia.org/wiki/Bergius_process
https://en.wikipedia.org/wiki/Fischer–Tropsch_process
[2] https://en.wikipedia.org/wiki/Battle_of_Stalingrad#Prelude
https://en.wikipedia.org/wiki/The_Motherland_Calls#/media/Fi...
https://books.google.ch/books?id=6_h3DwAAQBAJ&pg=PA85&lpg=PA...