Which of the following statements is true? soil forms from weathered rocks and organic material.fertile soil usually forms in areas with steep slopes.the o horizon is a dense layer of fine soil and clay.the higher the number of living organisms in an area, the less fertile the soil will be

Soil forms from weathered rocks and organic material. 
The rest of the statements are false. First, fertile soil usually forms in plains or lands with lower steepness of slope. Soil in steep slopes are prone to erosion.

The O-horizon is made of material derived from trees (i.e. leaves, pine needles), decomposed materials and humus.

Lastly, more living organisms in an area means more nutrients for the soil. 

Soil forms from weathered rocks and organic material is true other statements are false.

Soil forms from weathered rocks and organic material: This statement is true because soil is the aggregate of fine particles, which are formed from large rocks by the process of weathering. Weathering involves the break down of rocks into small particles due to the effect of wind, water and chemical agents. The organic matter is added by the decomposition of dead plants and animal matter.

Fertile soil usually forms in areas with steep slopes: This statement is false because fertile soil develops in the land with less steepness. As, the steep slopes the surface water run off takes away the superficial layer of fertile soil from the land.

The O horizon is a dense layer of fine soil and clay:  This statement is false because the O horizon is the horizon of soil, which exhibit undecayed or partially decayed plant and animal matter, the soil particles are fine but it lacks the synthesis of organic matter.

The higher the number of living organisms in an area, the less fertile the soil will be: This statement is false because, the fact that larger the number of living organisms in an area, the more the organic matter will produce due to the decomposition of carcass of animals, plant matter, human and animal feces. The organic matter will increase the fertility of soil.

Explanation:

Main functions of central nervous system ;

Connects the central nervous system

to the parts of the body.

Relays information and responses. Controls body functions.