Charles I's Death Sent Shockwaves Through Europe Because

Multiple Choice

Charles I's death sent shockwaves through Europe because:

A) he was killed by Cromwell in a particularly brutal way.
B) he was assassinated after he had surrendered to the parliamentary army.
C) it was the first time a reigning king had been legally tried and executed for treason by his subjects.
D) it was the first time a reigning king had been killed by his subjects.
E) he was killed by his own forces.