To determine the length of Andy's original line segment, we need to remember that the line segment bisector divides the segment into two equal parts.
If each piece is 2.9 centimeters long, then the total length of the original line segment is:
\[ 2.9 , \text{cm} + 2.9 , \text{cm} = 5.8 , \text{cm} \]
Thus, the correct response is:
5.8 cm