A major factor affecting crop yield is__________.

All of the listed factors—soil fertility, crop variety, and pest pressure—are essential elements that significantly influence crop yield.

Soil fertility refers to the nutrient content and the ability of the soil to sustain agricultural plant growth. Adequate nutrients, such as nitrogen, phosphorus, and potassium, are crucial for optimal plant development and yield production.

Crop variety plays a vital role as different species and hybrids can have varying levels of resilience to environmental stresses, pest resistance, and yield potential. The selection of suitable crop varieties can substantially enhance productivity based on local growing conditions.

Pest pressure is another critical factor, as pests can damage crops, reduce yields, and affect the overall health of the plants. Effective management of pest populations is necessary to minimize losses and maintain high yield levels.

Since all these factors contribute significantly to the overall crop yield, the correct answer encompasses the importance of each aspect in tandem, leading to the conclusion that their combined influence is paramount.