Humus is
A) Dead and decayed organic matter
B) Living matter
C) Fertilizers
D) Living animal,plants and microbes

Hint: In soil science, humus is the fraction of soil organic matter that is amorphous and without the cellular cake structure characteristic of plants and animals.

Complete answer:
Humus significantly affects the bulk density of the soil and contributes to the retention of moisture and nutrients. Although the terms humus and compost are informally used interchangeably, they are distinct soil components of different origins; humus is produced by anaerobic fermentation, while compost is the result of aerobic decomposition.

In agriculture, "humus" is sometimes also used to describe mature or natural compost extracted from a forest or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon containing organic matter (humus type, humus form,humus profile).

Humus is a dark, organic material that forms in the soil when plant and animal matter decay. When plants drop leaves, twigs, and other material to the ground, they pile up. This material is known as the leaf litter. When the animals die, the remains add to the litter. The thick brown or black substance that remains after most of the organic litter has decomposed is called humus. Humus contains a lot of useful nutrients for healthy soil.

Thus, the answer is option is option ‘A’ i.e, Dead and decayed organic matter.

Note: It is difficult to define humus precisely because it is a very complex substance that is not fully understood. Humus is different from the decomposition of organic soil matter. The latter looks rough and has visible remains of the original plant or animal material. Fully humidified humus, on the contrary, has a uniformly dark, spongy and jelly-like appearance, and is amorphous; it may gradually decay.