What is the main nutrition-related problem likely to be encountered by a vegan if his or her diet is not carefully selected?

I believe it is insufficient intake of vitamin B-12. 

1.controls blood flow2.controls oxygen flow3.carries oxygen rich blood to veins

Answer in 2009 barack obama signed into law the family smoking prevention and tobacco control act, the new law (h.r.   1256) represents the most sweeping action taken to date to reduce what remains the leading preventable cause of death in the united states;