在TPO Reading 16 Passage 3 - Trade and the Ancient Middle East的最後一段，第二句:
The central state, though often very rich and very populous, was intrinsically fragile, since the development of new international trade routes could undermine the monetary base and erode state power, as occurred when European seafarers circumvented Middle Eastern merchants after Vasco da Gama`s voyage around Africa in the late fifteenth-century opened up a southern route.
一開始看到as occurred when European seafarers circumvented Middle Eastern merchants after….
無法理解為何as會後面直接接一個動詞occurred，後來才知道as也能當作關係代名詞(https://reurl.cc/3ODN5O)
所以這裡as occurred = which occurred
as = which = the development of new international trade routes could undermine the monetary base and erode state power
算是學到一個之前不知道的用法了。
