Have no idea how this works

Imagine this, you send out a resume and get a reply within 20 minutes thanking you for your submission. And this is an actually reply from an actual person (or so you believe as far as you can tell) as opposed to some automated system reply. This gives you confidence that there is a real live person reading your carefully crafted attempt at the sale of yourself.

7 days go by and in your daily path of checking the usual suspect job sites you go back to the site where you found said job and it is gone. It was there 4 days ago (according to the Google Cache that is) but today it is not there. And you have had no further contact from since the initial "Thanks" email.

The job had been posted for over 2 months before you got around to submitting yourself. And now within the span of a week of you throwing your hat in the ring it has been filled. Or at least that is what you presume.

Do you....
A) Move on and work on writing a better cover letter and resume for the next opportunity?

OR

B) Contact original person with some kind of "Just wanted to check in, I see the job is gone from your website, am I out of the running?" kind of email?