参考答案

正确答案：A
解析：在美国，电来自于煤和自然气的比例有多少? 根据上题出处下面的内容Where will the electricity for the electrolysis of water come from?可以发现Currently，about 68 percent of the electricity produced in the United States comes from coal or natural gas．而about 68 percent表明大部分电都来源于煤和天然气。