题目

Since Jack was laid off from his job three months ago, he _____ a new one, but without luck.A. looked for B. had looked forC. has been looking for D. is looking for 答案：【答案】C【解析】考查时态。句意：自从杰克三个月前被解雇后，他一直在找个新的工作，但是不走运。时间状语是since引导的，主句应该是现在完成时或现在完成进行时，这里强调动作一直在进行而且可能还要进行下去，用现在完成进行时，故选C。室内火灾发生时，受困人员应采取弯腰甚至匍匐的姿势撤离，以尽量减少有害气体的吸入。这是因为燃烧产生的有害气体（　　）A. 温度较低，密度较大B. 温度较低，密度较小C. 温度较高，密度较大D. 温度较高，密度较小