This is a slightly difficult question. The passage talks about what modern Europe has done in order to adapt to changing international order. There are two things it has done: establish a common currency, and a formal political structure, adjusting its internal differences by peaceful mechanisms. 1 looks good, but does the passage say that "Europe has consistently done this"? Maybe. But what it misses here is the essence. Europe has changed its structure, but the focus of the passage is on "what it has done of late". For this reason, 4 wins. By choosing a common currency it has tried to lower economic heterogeneity, and by establishing European Union it has tried to lower political heterogeneity. Thus 4 captures the essence, while 1,2 and 3 walk on the periphery.