A Particular Difficulty Associated with Citing Material Sourced from the Internet

A particular difficulty associated with citing material sourced from the Internet in the text and in reference lists is that

A) it is not always able to be accessed due to technical problems.
B) the documents obtained may be either password protected or have authentication certificates.
C) different versions of the document may be placed on the same website over a period of time or the website itself may disappear.
D) web-based documents may be altered or tampered with rendering them unreliable or questionable for referencing purposes.