4. Researchers used two footballs of the same size to examine the effect of helium on kicking distance. One football was filled with air, and the other was filled with helium. Eleven people...

Extracted text: 4. Researchers used two footballs of the same size to examine the effect of helium on kicking distance. One football was filled with air, and the other was filled with helium. Eleven people participated in the study. Each person kicked the football filled with air and the football filled with helium, and the kicking distances, in yards, were recorded. The football that was kicked first was determined by the flip of a fair coin, and the people did not know which football was filled with air and which was filled with helium. What type of study was conducted by the researchers and, of the following, which is the appropriate t-interval for inference? (A) A completely randomized design and a t-interval for a difference between means for independent samples (B) A completely randomized design and a t-interval for a mean difference (C) A matched-pairs design and a t-interval for a difference between means for independent samples (D) A matched-pairs design and a t-interval for a mean difference (E) An observational study and a t-interval for a difference between means for independent samples