when. and that may happen at any time. norah. >> o'donnell: charlie d'agata, thank you. and another signal that an invasion may be hours away, two key airports in eastern ukraine are now closed. and as ukraine prepares, school children are getting survival lessons including how to identify explosives and the importance of bulletproof vests, helmuts and first aid. cbs' holly williams traveled to the front lines that was shelled earlier this week. >> reporter: this is irina yarmolenko, a factory worker filming herself. while her village was hit by shelling on monday night, and she hit hid deep in her basement. irina survived. so one hit there. and in her village, around seven miles from the front line, they're cleaning up the mess and patching up their homes. irina's apartment building is scared with shrapnel, its