题目

A summary of the physical and chemical nature of life must begin, not on the earth but in the sun; in fact, at the sun’s very center. It is here that is to be found the source of the energy that the sun constantly pours out into space as light and heat. This energy is liberated at the center of the sun as billions upon billions of nuclei hydrogen atoms clash with each other and fuse together to form nuclei of atoms. The output of light and heat of the sun requires that some 600 million tons of hydrogen be converted into helium（氦） in the sun every second. Thus the sun has been doing for已知，，，将a、b、c这三个数按从小到大的顺序排列为（    ）