What was a provision of the magna carta?

Assuming your options are king's power expanded, a step toward providing nobles with legislative authority, trial by jury of peers, and expanded rights to all English citizens, the correct answer is trial by jury of peers.
Magna Carta was a document made to reduce the power of the king, so the first option is definitely incorrect. Although the document was created to give more power to the nobles, they weren't supposed to have legislative authority, which is why that is incorrect too. The document didn't expand the rights of all English citizens, but rather only of nobles, so the last option is not true. This leaves us with trial by jury of peers, which meant that nobody could be imprisoned until he or she is judged in court first.