A researcher conducted the regression of stock return rate and obtained the following equation: , = 0.638 +0.402 x2,-0.891 x 31 y, (0.436) (0.291) (0.763) R = 0.96 R = 0.89 But he thinks there may be problems with this model. Consider their significance of the coefficients by calculating t-ratios, and figure out where the problem is and how to fix it. (Suppose the critical value of the T-statistic is 2)