【单选题】The availability of fixed nitrogen, an essential nutrient, may have limited the size of the primordial biosphere. As early cells acquired a capacity to fix atmospheric nitrogen, the biosphere expanded...
【简答题】By 2050 there will have been an extra 2.5 billion people on earth. And what will they eat? To solve the problem, we should have to double our food production. We can also develop a diet of algae(海藻), ...