GRE Text Completion: JiJing 1373-GRE填空机经1373题 - C8RUA2O07NH5269VA

Although scientific progress leads to constant revision of ideas, one observation that has remained ____________ over the years is that there are a lot of insects in the world: some 950,000 species have been identified. A. robust B. significant C. strong D. perplexing E. confounding F. obscure