Answer: d. 0.4
Step-by-step explanation:
We know that the correlation coefficient is a r-value measure of the strength of the linear relationship between two quantities.
When the value of correlation coefficient (r-value) lies between -0.5 to -0.3 or 0.3 to 0.5, then it indicates that there is moderate association.
From all the given four correlation coefficients , 0.4 is the best value that exemplifies a moderate relationship showing less back pain in people who exercise more frequently since it lies between 0.3 and 0.5.
Hence, d is the correct option.
