試題詳解

8. Naturally, all the nitrogen present in the nitrogen cycle comes from________.
(A) industrial fixation of nitrogen by producing artifcial fertilizers, which are then used to grow the crop.
(B) release of nitrogen during the litter decomposition process in the soil.
(C) nitrogen fixation activity of some organisms (e.g. bacteria associated with roots of leguminous plants), and lightning.
(D) emissions of nitrates from the cars, motorbikes and factories.
(E) decomposition of animal bodies.