Answer the following question:-
Noise is a common problem in both urban and rural areas, traffic noise in particular. Trees and shrubs are not only visually attractive but also can make effective noise barriers. Therefore when space permits we have to plant more trees and shrubs in areas where there is noise problem. By doing this noise can be reduced by six decibels over a distance of 30 metres. The only thing we have to keep in mind is that the planting should be particularly dense, the trees which have dense foliage and relatively vertical orientation of arrangements should be planted. It will completely screen the source of noise. If there is any gap in barrier it will still allow noise to penetrate. Single layer of trees is worthless as a noise barrier. Due to inter-reflection, multi-rows of trees are more effective.
"Single layer of trees is worthless as a noise barrier.' Why?

Options

A. Noise can't penetrate easily
B. Help in the growth of shrubs
C. Noise is sent back to the source
D. Noise can penetrate easily