Pre- study scores versus post- study scores for a class of 120 college freshman english students were considerated. The residual plot for the least squares regression line showed no pattern. The least squares regression line was y^=0.2+0.9x withwith a correlation coefficient r=0.76. What percent of the variation of post-study scores can be explained bt the variation in pre- study scores? A. 76.0% B. 52.0% C. 57.8% D. 87.2%.