Answer:
Roots of the trees that is present several yards from the pipes.
Explanation:
Roots of the trees that is present several yards from the pipes are responsible for the blockage of pipes because roots in the soil can penetrate to a large distances. The roots of tree moves a large distance in the soil for the absorption of water and nutrients so we can say that the group of trees that is present at the side of property is responsible for blockage of the pipes.