Usually a rectangular plate of material,capacitors are essential

Usually a rectangular plate of material,capacitors are essential to electronics because they can perform tasks that batteries can't.Each contains a material called a dielectric,which can store electrical energy and then release it in a large burst.
【正确答案】：电容器通常是一块矩形材料板，是电子器件的重要无件，因为它们能完成电池所不能完成的任务。【解析】原句是主从复合句，because 引导的是原因状语。usually are rectangular plate of material 是capacitors的同位语，对其进行补充说明，汉译时译作一句话，essential 汉译时转化为名词“重要元件”。