What I found is that written evidence for knocking on wood (and for the history of gesture as a whole) is remarkably sparse. In the Penguin Guide to Superstitions, folklorist Steve Roud offers a skeptical take on the provenance of knocking on wood due to the near total absence of written records about it:
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现在只是拿到临床试验申请批准，接下来要走 I、II、III 期试验，按行业规律，最快 5-8 年才能上市。长春高新现在的状况，能不能撑到那时候都不好说。。同城约会对此有专业解读