This question seems to give quite a lot of students trouble. So I am posting a quick solution of how to attack this question from LSAT prep test 83, in section 1 of the Logical Reasoning section of the test.
Line Reference: The traditional view of the Roman Emperor Caligula
Strengthen: Strengthening an argument means to cement the connection between evidence and conclusion. In other words, it means to make the conclusion more likely to follow from the evidence.
Conclusion: Some modern historians do not think that Roman Emperor Caligula was a cruel and insane tyrant
Evidence: There is not a lot of documentation of the alleged cruelty and the histories that we do have were written by his enemies
Analysis: Lack of evidence (documents) does not prove something did not occur. Perhaps the documents of his cruelty were destroyed by the Emperor? However, we are looking to strengthen this argument and help prove this Emperor was not necessarily cruel. So, the right answer could eliminate ideas that would hurt the argument (disprove point I made above). But, they just have to be any piece of evidence that would make it less likely this Emperor was cruel. Often strengtheners can be hard to predict
A) Having less documentation from his era than others does not help our argument. If anything, it would weaken it – it could be pointing out that he destroyed documents! This is likely a weakener
B) We do not know how the people who lived under this Emperor viewed him for sure. So this point would not help or hurt the argument – it is just irrelevant
C) CORRECT – if the cruel acts assigned to this Emperor are almost identical to the acts assigned to other rulers that are labelled a tyrant then it makes it less likely the Emperor actually did these things. It increases the chance that the alleged acts are actually made up, if documents all say the same thing about everyone. This is increasing the chance that all these documents are suspect if they say the same stories about everyone. Feels more like a story than fact. Keep in mind, this is a weak strengthener – it definitely does not prove he definitively was not a tyrant, but that is okay. A strengthener only has to increase the chance the conclusion is true by 1%
D) If the documents believe this Emperor was crueller than most that would weaken the likelihood that he was not a tyrant
E) It does not matter if there are worse tyrants out there today. Just because someone is more cruel than you does not make you nice.