There were lot of organisms A in the crop fields in an area. These organisms used to feed on organisms B also present in the crop fields but which damaged the standing crops. One day some people arrived in the fields and killed all the organisms A so that they could remove their C for making fancy items which were in great demand. Due to large scale killing of A, the population of B increased too much damaging all the crops in the area and causing a famine-like situation. Apart from A, there is another organism D which can also kill and eat B. Name A, B, C and D.

The organisms which are in great demand for making fancy items are snakes. Their skin is in great demand. Organisms which cause damage to the crops are mainly rats. Since earlier snakes ate rats the crops were not damaged. But after humans killed snakes for their skin, rats thrived and destroyed the crops. However, apart from snakes rats can also be killed and eaten by cats. So,

A:snakes, B:Rats, C:Skin and D:Cat


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