The last thirty years _____ the greatest number of laws stopping our rights and progress,until today we

have reached a stage ____ we have almost no rights at all.[ ]

A. saw; which

B. have seen; that

C. saw; where

D. have seen; where

按体积计算，空气中含量最多的气体是______．空气中两种主要气体的体积比大约是______．