The correct answer should be additionally.
The word additionally would provide the best transition between these two sentence. It is so because you have one idea in the first sentence, and then you want to show another idea very similar to the first one in the second sentence. Using additionally to convey that is the way to go.
Most likely audience and purpose. It's not like there are timed applications and the way you write it is up to as long as it makes sense.
It is A because itis not it;s means it is and that would not make sence
