Sources B and D were both written in different time periods. One was written in 1794 and the other was written 2 years later in 1796. Source B was written by Robespierre in 1794 so it was at the time of the revolution which would make it reliable because it is not being written out of hindsight and because Robespierre knows what is actually happening and to what extent things are happening.
This source was written as a speech so it was meant for members of the public and not just for one person’s eyes, which means that it had to be accurate as many of the people in the convention would have known what was really happening so he could lie about the event of things. Source D was written in 1796 so again was at the time of the Revolution which again is a good thing because it means that it is not written retrospectively, so again nothing said could have been changed due to the writer’s view of things.
It was written by a lawyer so it was a well educated person that came from the Middle class which may mean that the source is biased as they could be defending their class but they may not. This source can be reliable because he was there at the time and this was the time of Robespierre fall from power in 1796, so this could have influenced their view of things. Both of these sources can be said to be reliable because there
Source C was written by an American representative in Paris in 1791, this source is not going to be the most reliable because it was just one persons view and he was an outsider to all of this so had no real input in the events of the revolution, but could be said to be reliable because he was in Paris and was there when it was happening so he would have known what was really going on.
This source could be said to be biased because it only gives a positive and favourable view of the King there are no contrasting arguments so you don’t really see the whole picture and he could be making up how good Louis was just because he like him and thought highly of him. Source D was written in 1972 and was again written by and outside but this time a British ambassador and this source again can be said to be unreliable because it was also only written by one person so again only shows what he ants to show, but again could be reliable because he was there at the time of all of these events. This source could also be said to be biased because it again gives one opinion but an opposite one to the American but is still biased because he could also be making things up to make Louis look worse than he actually was. Out of the two sources I would say that both sources are as useful and reliable as each other and as unreliable as each other.