题目

There are two types of people in the world. Although they have equal degree of health and wealth and other comforts of life, one becomes happy and the other becomes unhappy. This arises from the different ways in which they consider things, persons, events and the resulting effects upon their minds. People who are to be happy fix their attention on the convenience of things: the pleasant parts of conversation, the well－prepared dishes, the goodness of the wine and the fine weather. They enjoy all the cheerful things. Those who are to be unhappy think and speak only of the opposite th如图所示，直线AB和CD表示彼此平行且笔直的河岸．若河水不流动，小船船头垂直河岸由A点匀速驶向对岸，小船的运动轨迹为直线P．若河水以稳定的速度沿平行河岸方向流动，且整个河中水的流速处处相等，现仍保持小船船头垂直河岸，由A点匀速驶向对岸，则小船实际运动的轨迹应该是图中的（ ）A．直线RB．曲线QC．直线PD．曲线S