Failing to accurately cite even a single source
a. can result in accusations of plagiarism.
b. will definitely result in errors with other citations.
c. isn't an error that will cause problems for the author.
d. will certainly cause problems with the logic of the essay.
Failing to accurately cite even a single source "a. can result in accusations of plagiarism" since even if this is not your intention, it is very hard to prove it when being examined.
