Answer:
The option that shows the best revisions to create sentence variety is:
C. History interests me. I decided to read the Declaration of Independence.
Step-by-step explanation:
The two original sentences are very focused on the subject, which happens to be "I" in both. That makes them sound repetitive. The best way to create variety without combining the sentences would be to change one of them by taking the focus away from "I". The option that does precisely that is letter C. The original "I am interested in History" is changed into "History interests me." This revision makes "History" the focus of the sentence, thus creating variety.