Crutzen has suggested that the Antropocene began in the late 18th century, when, ice cores show, carbon dioxide levels began what has since proved to be an interrupted rise.
此处的ice cores show为什么要作插入语,另外有begin后可以接宾语分句吗?
How silly it is to travel out by high-speed rail _____you can take a plane,whichis much cheaper.A.while B.when C.since D.though答案选B,可是C有既然的意思也能说通为什么不选?