Ilya had the following hypothesis: > There is a negative linear (or almost linear) association between the average heart rate of a mammal species and the species' average life span. He conducted a study to test his hypothesis: > He found an article in a respectable magazine that lists the average heart rate (in BPM - Beats Per Minute) and average life expectancy (in years) of hamsters, chipmunks, rabbits, cats, pigs, and horses. He used this data to obtain the following scatter plot, which is almost linear: $\quad$ **What type of statistical study did Ilya use?** [[☃ radio 1]] **Was Ilya's study conducted in an appropriate way? Mark the most suitable choice.** [[☃ radio 2]]