Dear Pablo: I have been wondering for some time what a life cycle analysis would show is the "greenest" way to ship milk. Plastic containers are light, but are not reusable and don't biodegrade; cardboard containers are less light, are not reusable, and don't biodegrade either. Glass bottles are reusable, but are really, really heavy--and so, of course, use much more fuel to ship. My local coop carries all three, and I am conflicted every time I shop. What should I do?