题目

阅读理解Yourbest friend that follows you around when the sun comes out - your shadow -doesn't serve an important function like your heart or brain, but what if youcould use shadows to create electricity? When using solar panels (电池板) that are powered by light, shadows can be boring because it meanselectricity can't be created. However, researchers from the National Universityof Singapore have engineered a way to create power from the shadows presenteverywhere.Ateam of the university created a machine that can collect energy from shadows.It is created by placing a thin coating of gold从物质循环的角度看，人体内的碳元素最终来自（ ）A.动物体内的碳B.大气中的二氧化碳C.燃煤中的碳D.植物体内的碳