Final answer:
The line that illustrates Bess's desperation to warn the highwayman is: "Up she stood to attention, with the muzzle beneath her breast."
Step-by-step explanation:
The line that illustrates Bess's desperation to warn the highwayman that the redcoats set a trap for him is:
"Up she stood to attention, with the muzzle beneath her breast."
By standing up to attention and pointing the muzzle of the gun towards her own chest, Bess is willing to sacrifice herself in order to warn the highwayman about the trap. This action shows her desperation and determination to save him.
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