A substance, such as water or graphite, that is used in a nuclear reactor to decrease the speed of fast neutrons and increase the likelihood of fission.
慢化剂一种物质，如水或石墨在核反应堆中用来减缓中子运动速度和提高裂变可能性的物质
graphite is used in making lead pencils.
石墨常被用来做成铅笔。
graphite is a soft black substance.
石墨是一种软而黑的物质。
