如图是医用回旋加速器示意图，其核心部分是两个D形金属盒，两金属盒置于匀强磁场中，并分别与高频电源相连．现分别加速氘核（ ${}_1^1$ H）和氦核（ ${}_2^4$ He）（认为这两种粒子比荷相等）．下列说法中正确的是（   ）

   A plant makes its own food in its leaves . Water comes to the leaves through the roots . Air gets into the leaves through very small holes . The green coloring in the leaves uses the water and air to make the food for the plant . It also needs sunshine because a plant can make food only when the sun is shining.
   Animals and people could not live without green plants . They both eat plants . People and some animals also eat the meat of some animals and these animals eat plant

读如图漫画“小草的哀求”，漫画所反映的情况可能导致的环境问题主要是（　　）