BEIJING — The departing U.S. ambassador on Tuesday defended a tough approach to China that has riled relations between the world’s two largest economies, saying the Trump administration has made progress on trade and that he hopes that will extend to other areas. Terry Branstad, the longtime Iowa governor chosen by President Donald Trump to be envoy to China, agreed however that China has generally reacted to pressure by responding in kind, from closing consulates to imposing import tariffs.