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答案：E
解析：
A line that is parallel to the x-axis and four units above the x-axis is the vertical translation of the x-axis four units upward. Since the x-axis is a horizontal line and has equation y = 0, it follows that the line parallel to the x-axis and four units above the x-axis has equation y = 4.
adj. 垂直的，顶点的，纵向的
n. 垂直物
