The annual return on a stock is normally distributed with a mean of 15% and standard deviation of 20%. With 68% confidence, we should expect its actual return in any particular year to be between which pair of values? (Hint: Look again at page 12 of lecture note 1 .) a. 5% and 35% b. 25% and 55% c. 45% and 75% d. 50% and 80%