syllables, we did a water color art project. >> reporter: and while it's the first time these kids have had a sub in uniform-- >> that's green, and purple. >> reporter: --they do seem to like their new commanding officer. >> she's a very good teacher and she's very kind. >> reporter: all new substitutes go through a background check and online training course. colonel corona tells us she has a newfound respect for teachers. she calls them real heroes. and norah, we can confirm, the colonel did not forget to give out the homework assignments. >> o'donnell: of course she didn't. all right, kris van cleave, thank you so much. and we learned today that in the last 24 hours, there has been an increased russian buildup of troops on the ukraine border. also, the u.s. military naming the ten u.s. bases where some 8,500 troops are on heightened alert to deploy to eastern europe. cbs's holly williams reports from ukraine's capital of kyiv. >> reporter: the u.s. says the