Final answer:
To find out which cousin can throw a ball the farthest, conduct multiple trials with each cousin under the same conditions and measure the distances.
Step-by-step explanation:
To find out which cousin can throw a ball the farthest, Tenesha should conduct multiple trials with each cousin under the same conditions and measure the distances. This option, C, will provide the most accurate results because it eliminates bias and takes into account any variations in throws. By conducting multiple trials, Tenesha can determine the average distance thrown by each cousin and compare the results to determine who can throw the farthest.