48.we 49.from 50.because / as / since 51.than
52.hard / difficult 53.other 54.or 55.but
略
根据文章内容填空，每空一词。Humans are responsible for causing changes in
48.we 49.from 50.because / as / since 51.than
52.hard / difficult 53.other 54.or 55.but
略