The correct answer to this open question is the following.
There is no question at all. This is just a quote. The question is missing.
Doing some research, the question should be "Which of the following documents addressed Blackstone’s concern in this quote?
You also forgot to include the options. However, we can say the following.
The document that addressed Blackstone’s concern in this quote was the Magna Carta because this important English document limited the power of the British King.
King John of England had been a tyrant and an oppressor. Barons of England and other classes were tired of him and drafted the Magna Carta to limit his power and despotic control. The King had to sign the document in 1215 to avoid an open confrontation or a possible rebellion. Magna Carta included rights and liberties for the barons and made the King accountable for his actions.