A.) The subject was dropped, but it was clear that it would be brought up again.
The first sentence is the most exact and the most precise because of how the idea is communicated in least amount of words possible. It is important to keep in mind that when you are writing something that comprehension always goes down the more words there are in a sentence. Thus, it is always best to communicate with the fewest words possible. Let’s take a look at another example. Say you are at a baseball game and a fly ball is coming directly toward you without your knowledge, and the person sitting next to you tries to warn you by saying the following: “Because of the velocity of a baseball coming in your direction and the potential damage it may cause if it comes into contact with your head because you are not wearing a helmet and because ambulance rides as well as emergency room visits are not fun nor cheap, you should probably seek to get out of the way as soon as possible.” How would that work? Now, compare that to the more exact/precise sentence of “Duck!” See how that works?