To solve this question, the user needs to understand the correct preposition to use after the phrase "in addition".

The correct preposition to use in this context is "to", making option C the correct answer.

Explanation of each option:

A. "In addition" can be used alone as a phrase, but it does not take the preposition "of". This option is incorrect.

B. "In addition of" is not a correct phrase in English. This option is incorrect.

C. "In addition to" is the correct phrase that indicates the addition of something to something else. This option is correct.

D. "In addition from" is not a correct phrase in English. This option is incorrect.

Therefore, the answer is: C. in addition to.