Final answer:
The length of a line segment is unaffected by translation; it remains constant irrespective of the translation's direction or magnitude.
Step-by-step explanation:
The length of a line segment remains unchanged during a translation because a translation is a type of transformation that shifts a figure into a straight line without altering its size or shape. Therefore, if the line segment is translated 2 units down and 4 units right, the length of the resulting line segment would be the same as the original segment. The options provided (a) 5 units, (b) 9 units, (c) 11 units, and (d) 17 units do not apply here as the question describes a translation, not a measurement of the segment. We need more information about the original length of the line segment to determine how these options relate to the question.