Answer:
a)D. Since the company wants to predict revenue from advertising expenditure, the explanatory variable is advertising expenditure.
b)B. Since the company wants to predict revenue from advertising expenditure, the response variable is revenue
c)C. Since advertising expenditure is the explanatory variable, it should be plotted on the x-axis.
Step-by-step explanation:
a) The explanatory  variable is the independent variable (the difference between explanatory an indepent is that independent means that it doesn´t depend of any variable at all and in the explanatory  variable we are not 100% sure)
In this case, the  company wants to know if the money they spend in advertising  is related to the company's revenue. So , in this case the  explanatory variablle is the money they spend in advetirsing  while the dependent variable is the revenue ( that will increase or decrease depending on the money spent)
b) The response variable ist he dependent variable so like it was explained in a) is  revenue.
c) In a cartesian graphic on the x axis we always draw the independent variable, so in this case we will draw the money spent in advertising.