Use the current perfect tense to advise that something has transpired much more than when up to now and may be continuing; for instance, "In the final twenty many years, scientists have generally concentrated on the effects of posttraumatic anxiety dysfunction." 文献综述也叫研究综述、国内外研究现状，是指在全面掌握分析某一学术问题或者研究领域相关文献的基础上，对该学术问题或研究领域在一... http://literature-review91234.blogkoo.com/a-simple-key-for-unveiled-29958154