The conclusion that the fertilizer is a significant improvement because it increases yield by 20% is most likely influenced by:
D. a Well-designed experiment.
A well-designed experiment would ensure that the results are valid and reliable, taking into account control variables, randomization, proper sample sizes, and appropriate statistical analysis. This would provide credible evidence to support the claim that the fertilizer leads to a significant increase in crop yield.
While options A (precise measurement) and C (replication) are also important factors that can contribute to the strength of a conclusion, the most direct influence on the conclusion itself in this context would stem from having a well-structured and executed experimental design. Option B (a value judgement) would typically refer to subjective opinions rather than empirical evidence.