The weather turned out to be fine yesterday. I ______ my umbrella with me.[ ]

A. would have carried

B. could have carried

C. needn't have carried

D. mustn't have carried

发生水灾事故时，除分析计算被堵人员所在空间体积，（）浓度是计算出遇险人员最短生存时间。

A.O₂

B.CO₂

C.CO

D.CH₄