随堂演练及时体验 巩固提升 ⅰ.完成句子 1.this custom ________ ________ ________ (追溯到) the 17th century. 答案 dates back to 2.he went over to america ________ ________ ________ ________ (目的是为了) studying medical science. 答案 for the purpose of 3.some people believe that one's personality ________ ________