ⅰ.完形填空 london's river thames has twentyseven bridges. tower bridge, the first bridge over the thames as you travel towards london from the sea, is the__1__of them all. the thing that is surprising about__2__is that it opens in the middle. it does this to let the big ships__3__to the pool of london. if you are__4__enough to see the bridge with its two opening arms high in the air,
