What are groups of organized citizens that seek to achieve political power and influence within a government called?
a. democrats
b. political parties
c. special interest groups
d. political leagues

The best answer here is b. political parties: they are groups of citizens (anyone can join) who seek to be part of the government. 

Other options:
Democtrats are an example of a political party
Special interest group is a bit similar in that it unites people with the same interest, but they do not seek power in the government, but rather some advantages, for example a specific law.