According to the theory of optimal currency areas, which of the following criteria among a set of economies would render them a good candidate to form a currency union? (a) Economies which are fairly closed off from one another (b) Economies in which DD shocks across countries are perfectly positively correlated 4 (c) Economies in which fiscal resources can be fairly easily transferred across borders (d) (a) and (c) (e) (b) and (c) (f) All of the above