Choose one word or phrase from the bracket to make the sentence more formal. The number of mature female green turtles that return to their primary nesting beach has _________ (decreased; gone down) from 1,280 ten year ago to 145 today.
【简答题】—How long have you been in this office? —Just a few minutes. Mycousins_______here together with me. A. havewalked B. had walked C.walked D.have been walking