None of the above
a) is too passive aggressive, and when it turns out the friends in question all have perfectly valid reasons for not getting in touch (phone fallen in deep fat fryer rendering it unuseable, tractor ran over foot and have therefore been in hospital, dog has just died in a horrible blender accident, etc) you will feel like a twunt, and a snidey one at that.

b) as above but you would just feel like a twunt, not a snidey one.

c) actually you could use this, as at least you could to pass it off as genuine thoughtfulness if necessary. But deep down you'd know that you shouldn't have jumped to conclusions, and are therefore a twunt.

EDIT: Of course when it turns out they are just plain ignorant, you can then claim the moral highground and legitimitely act the injured party, having not directed any blame first.
( warmfuzzies Isn't here, Wed 27 May 2009, 19:12, Reply)