I would like to inform you that your product is faulty. Put simply, it doesn't properly work. If you wished to maintain a formal tone in this message, which choice would make the best next sentence? A) This causes me great vexation. B) You won't believe how angry I am! C) I don't want to hear about how this just a simple mistake, either. D) I've followed the directions, but still get nothing but a big headache.
