A sales manager develops a regression model to explain the monthly sales volume of the company using the monthly advertising expenditure and the inflation rate in the economy as the predictor variables. Which of the following hypotheses should be used to test whether the overall model explains any variation in sales at all?

a) H is proportional to B1 and B2 , Ha : B1=B2=0

b) Ho : B1 not equal to B2 , Ha: B1

c) Ho : B1 not equal to B2 , Ha: B1 = B2

d) Ho : B1=B2 = 0 , Ha : atleast one coefficient is non zero