题型:选择题 —Your spoken English is so good. Have you been abroad?—Yes. I in London for two years.A.have stayedB.stayedC.had stayedD.have been staying 查看答案
题型:单项选择题 危险废物安全填埋,如果黏土土壤渗透系数为10-6~10-7cm/s,应采用人工防渗材料的渗透系数应为( )。A.<10-7cm/sB.<10-10cm/sC.<10-11cm/sD.<10-12cm/s 查看答案