As food moves through the digestive tract it spends the most time in the:

Cells destroy body cells infected by a virus or bacteria. killer t t memory t none of the above

Eutrophication caused by human nutrient pollution.

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled