Read the passage carefully and answer the question that follows. 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. The planted trees must be taller. We can reduce noise level by 1.5 decibels with each additional 3 feet of tree height When the opportunity to use trees is restricted a combination of shrubs and tall grass can be used. Instead of tarmac or gravel surfaces soft grass ground cover is preferable. It will absorb noise rather than reflect it. Rows of trees, shrubs, crotons, ground covering plants, climbers and their flowers not only reduce noise and provide a beautiful backyard they also help block wind, provide shade, and absorb traffic pollution.
Higher the trees

Options

A. higher the noise
B. lower the noise
C. greater the decibels
D. thinner the air