日语
韩语
法语
德语
西班牙语
意大利语
阿拉伯语
葡萄牙语
越南语
俄语
芬兰语
泰语
第一节 单项填空（共15小题；每小题1分，满分15分）
21.Some students think that learning a foreign language is slow and difficult-think of all the hours of hard work ______ they have spent learning English．
A．when B．in which C．that D．while
21.Some students think that learning a foreign language is slow and difficult-think of all the hours of hard work ______ they have spent learning English．
A．when B．in which C．that D．while
