The first alternative is correct (A).
The opening of an argument is important to introduce the way in which the author will deal with a certain subject. This is a way to prepare the reader to receive an opinion. In other words, in opening the argument the reader can identify if the author is against or in favor of the topic discussed. In this way, the reader can hear the argument knowing that the author will defend a point of view. This will cause the reader to question and reflect to agree or disagree with the author.