Consider the followingregression model between the dependent variable, SALES (reflecting monthly sales, in thousands of dollars) and independent variable, ADVERTISING (representing the monthly advertising expenditure, in thousands of dollars):

Estimated SALES = 8.1 + 1.9 ADVERTISING.

The value 8.1 in the above regressionline represents:

Select one:

a. the estimated value of SALES when ADVERTISING is zerob. a ratio of SALES over ADVERTISING as a percentagec. the change in SALES, on average, following a unit increase in ADVERTISINGd. the proportion of the variation in SALES explained by variation in ADVERTISING