亚洲国产精品VA在线赏，成人AV精粹成人在线免费享-人人操人人_婷婷五月天在线_五月天小说_久久人人爽人人爽人人片av高清_一本久久综合亚洲

In a mixed flow of oxygen and nitrogen, the lowest oxygen content required to maintain the combustion of the material is called the oxygen index. A higher oxygen index indicates that the product will not burn easily.