原文:二十世纪七十年代以来,国际经济形势发生了急剧的变化
译文:Since the 1970s, international economic situation has changed radically.

原文:二十世纪七十年代以来,国际经济形势发生了急剧的变化
译文:Since the 1970s, international economic situation has changed radically.

Since the 1970s, radical changes have taken place in the international economic situation.(考点:主语的转换)