Research has found that the drug contains a toxic chemical that can cause respiratory problems.研究发现，这种药品中含有一种有毒化学物质，可引起呼吸系统的毛病。It had been known for some time that chemical reactions can be catalyzed by materials with large surface areas.人们早已知道，如果材料的表面积足够大，可引起催化反应。