要使排尘效果最佳，必须使风速大于最低排尘风速，低于粉尘二次飞扬的风速。
参考答案：对
We forgave his bad temper because we knew that his son's illness had put him under great _____.
A．emotion
B．excitement
C．crisis
D．stress
黄曲霉素是一种（）
A.本身具毒性
B.内酯开环
C.氧脱烃化反应
D.杂环氧化
E.代谢后产生环氧化物，与DNA形成共价键化合物
