Online encyclopedias may contain a. video c. links to other informational sites b. images d. all of these

The answer is 
d. All of these

I would personally say D, all of the above.
The one thing I'm thinking is controversial is Images, because sometimes those can be fake and unreliable with information.

 But you could definitely find videos and links, so I would say D. All of the above

Be a little more specific