You Can Visit the Official Website of Any Large Restaurant $\alpha$

You can visit the official website of any large restaurant chain to examine the nutritional data for menu items. For fast-food restaurants, many menu items are high in fat, so most of their calorie content comes from fat (rather than from carbohydrates or protein) . Here we investigate the relationship between the amount of fat in a menu item (in grams) and the number of calories. To predict the number of calories in a menu item given its fat content, we use the simple linear regression model calories = $\alpha$ + $\beta$ (fat) , where the deviations are assumed to be independent and Normally distributed, with mean 0 and standard deviation $\sigma$ . The explanatory variable in this study is:

A) number of calories.
B) fat content (grams of fat) .
C) the slope, $\beta$ .
D) 12.546.