B. To guard the tree of life. As part of their punishment they were banned from ever eating of that tree or the tree of knowledge of good and bad. Eating from the tree of life would technically give them a legal right to live forever but because of their disobedience it was a privilege they had no right to have. God in the bible has a very clear legal/seniority/defined Justice it's humans who muck it up.It takes study but it can be interesting to read. Have an awesome day!