Refer to the given figure showing the pyramid of numbers in a certain habitat. Select the option that correctly identifies A, B, C and D.

	A	B	C	D
1.	Tree	Insects	Large birds	Small birds
2.	Phytoplankton	Small fish	Large fish	Fish-eating birds
3.	Tree	Insects	Small birds	Large birds
4.	Grass	Grasshopper	Frog	Snake

Pyramid of numbers is the diagrammatic representation of the number of individuals in different trophic levels. The given pyramid of numbers is spindle-shaped. It represents the pyramid of numbers of a tree ecosystem. A single tree is the producer. Many insects feeding on the tree are more in number. The number of small birds feeding on the insects would be fewer than that of the insects. The number of large birds eating the small birds would be still lower.