Concept:Crop improvement focuses on developing better plant varieties through breeding and selection.
Explanation:The main aim of crop improvement is to produce crops that give higher yields and better quality produce.
Improved varieties are developed using methods such as selective breeding, hybridisation, and genetic engineering.
These methods help combine desirable traits like increased yield, better nutritional value, and improved market quality into new cultivars.
While resistance to pests and diseases and tolerance to environmental stress are also targeted benefits, they serve as supporting objectives rather than the primary goal.
Expanding cultivation areas and increasing diversity are management or conservation practices, not the core purpose of crop improvement.
Therefore, the central purpose remains enhancing the quantity and quality of crop output.
Answer:D. Enhancing crop yield and quality