The correct option is D Eucalyptus trees should be planted near sewages as their smell can keep the insects away.
The amount of putrescible organic material in sewage is specified by the biochemical oxygen demand. More the amount of organic material more will be the biochemical oxygen demand.
Plants require phosphorous and nitrogen to grow. These are present in domestic sewages and can lead to excessive growth of algae.
Eucalyptus can absorb the excess water from the sewage and should be planted near it.