The length of a line segment does not change when the segment is translated.
Since line segment PQ is translated to form P'Q', the length of P'Q' is the same as the length of PQ.
Without the specific length of line segment PQ provided, I cannot give a numerical answer. However, we can conclude that if you know the length of PQ (let's denote it as L), then the length of P'Q' is also L.
If the problem states to choose from options A through D, it would be necessary to know the original length of PQ to select the correct answer. If you can provide the length of PQ, I can help you determine the length of P'Q'.