题目

. Each week, this program explains the many meanings of English expressions. Today’s expressions include a very important word—“heart”. We will try to “get to the heart of the matter” to better understand the most important thing about words and their stories. So “take heart.” Have no fear about learning new expressions. Besides, popular English words can be fun. There is no need for a “heavy heart.” Such feelings of sadness would only “break my heart,” or make me feel unhappy and hopeless. Now, let us suppose you and I were speaking freely about something private. We w物体竖直上抛后又落向地面，设向上为速度的正方向，则它在整个过程中速度v跟时间t的关系是图中的哪一个 （空气阻力不考虑）