The best way to tackle a source based question is to use CATPAD. In this:
C: Content, i.e. what is actually in the source
A: Author, i.e. whow wrote it, if they had any pre-exisiting beliefs you know about
T: Tone, i.e. the inflection of words and ideas they are therefore trying to portray
P: Purpose, i.e. why the author created the source in the first place, if they have any ulterior motives.
A: Audience, i.e. who the source was written for, can be linked to purpose closely
D: Date, i.e. when the source was written and if this has any historical importance, for example whether it was written before of after the Russian Revolutions of 1917.
If a source question asks you to compare the soruces it is impoartant you compare then on these levels and that you do not bunch the sources into types and only compare them in these bunches - try to compare as many as possible in as many different ways as possible.