Few candidates attempted this question. In 3(a) (i and ii), many candidates could not distinguish between straight fertilizers and compound fertilizers and give examples of inorganic fertilizers. In addition to this, in 3(c), many candidates were unable to state ways by which the carbon cycle is important in agriculture.
However, in 3(b), majority of the candidates were able to list the biotic and climatic factors that influence agricultural production in West Africa.
The expected answers include:                                           
Distinction between straight fertilizers and compound fertilizers
Straight fertilizers contain one major plant nutrient in the form available to plants
Whereas,
Compound fertilizers contain two or more of such nutrients.
                                                                                                           
Examples of inorganic fertilizers

• Sulphate of ammonia/ammonium sulphate
• Sodium nitrate
• Muriate of potash
• Single Superphosphate
• Triple superphosphate
• Urea
• Magnesium sulphate
• Crude potash salt
• NPK

Ways by which the carbon cycle is important in agriculture

• Helps in the manufacture of carbohydrates in plants
• Helps to purify the atmosphere by removing carbon(iv)oxide
• Animals and man eat up plants and plant products which they digest into food nutrients for body physiological processes
• Plants make use of part of these carbohydrates for their metabolic activities and store the rest in their protoplasm and in special storage organs.
• During aerobic respiration, oxygen is taken in it and it is used to break down the digested carbon compound within the cell. This results in the release of energy used by farm animals for work
• Decomposition of organic matter also releases humus
• The colloidal nature of humus enables it to improve soil structure
• Minerals salts in the soil improve soil fertility