题目

So difficult ______ it to live in an English-speaking country that I determined to learn English well.   A. I have felt                      B. have I felt                       C. I did feel                          D. did I feel 答案：D3．两辆游戏赛车a、b在两条平行的直车道上行驶．t=0时两车都在同一计线处，此时比赛开始．它们在四次比赛中的v-t图如图所示．哪些图对应的比赛中，有一辆赛车追上了另一辆（　　）A．A和CB．B和CC．A和DD．A、C和D