题干
阅读短文，选择恰当的答案。
Tomorrow is Saturday. Ben isn't going to school. He is going to get up early. In the morning, he is going to Xinhua Library .He's going there by bus. He's going to have lunch in KFC. The KFC is near the Xinhua Library. In the afternoon, he is going to play ping-pong with his friends. At about 4:30, he is going home to do homework. Then he is going to water the flowers .He's going to cook the meals for his parents in the evening.
Tomorrow is Saturday. Ben isn't going to school. He is going to get up early. In the morning, he is going to Xinhua Library .He's going there by bus. He's going to have lunch in KFC. The KFC is near the Xinhua Library. In the afternoon, he is going to play ping-pong with his friends. At about 4:30, he is going home to do homework. Then he is going to water the flowers .He's going to cook the meals for his parents in the evening.
为坐标平面内三点，O为坐标原点，若
方向
满足的关系式为 （ ）
