In the picture below I noticed there are three circles or holes of some kind ahead of the wing, what are those?
Thanks to a link from Jonathan Walters, here is a closeup of one:
The four smaller areas in a row along the centerline are the radar altimeter transmitters/receivers. The radar altimeter uses radio waves to determine the aircraft's altitude above the ground. This diagram for the A345 has them further aft, they're in similar configurations on other aircraft.