D all of the above, but they were just results of flawed strategy.
France after WW1 was so keen on not fighting again (due to great casulties, and the sheer horror of trench war), that it build great defences on it's frontier with Germany (Maginot line), and thought that she is safe behind them.
French army was defensively orientated, and was not prepared for bold manouvers of Blitzkrieg.
