A-horizon of the soil is also known as

Answer: Option D

The A horizon is the top layer of the mineral soil horizons, often referred to as ‘top soil’. This layer contains dark decomposed organic matter, which is called "humus." A horizon contains less clay or pedogenic oxides.
The A is a surface horizon, which is the home for various microorganisms as well as earthworms, thus it is the zone in which most biological activity occurs.