In the following passage some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.
Comprehension:

The interior of the Earth has three chief layers. (1)_______are known as the crust, the mantle and the core. There is a thick layer of soil (2)______ the outer crust. It is found only in (3)______ parts of the Earth. It consists of disintegrated rock and (4)______ organic matter called
humus. It is this soil which is indispensable for the plant (5)______.