B. It acts as a transition to connect the two sentences.
"In addition" is a linking or transition word whose purpose is to help the reader progress from one significant idea to the next in a more easy-flow way, meaning that it helps to connect two sentences or ideas. There are different types of transition words or phrases, "In Addition" is an "Additive transition". Transition words in this category tend to be placed at the beginning of a sentence, and their aim is to add another idea or further develop the previous point, as it occurs in the passage.