When they are hung telephone lines are allowed to sag?

Telephone lines are longer in a warm summer and shorter in a cold winter. Hence, they sag more on hot summer days than in winter. If the lines are not strung with enough sag in summer, they might contract too much and snap during the winter, especially when carrying ice. Also, a wire suspended between two points must sag because it's physically impossible for the sag to be zero.

D.na is the answer hope this