A program contains a void function named getNewPrice. The function receives two double variables named oldPrice and newPrice. The function multiplies the contents of the oldPrice variable by 1.1 and then stores the result in the newPrice variable. Which of the following is the appropriate function prototype for this function? 

a. void getNewPrice(double, double); 

b. void getNewPrice(double &, double); 

c. void getNewPrice(double, double &); 

d. void getNewPrice(double &, double &);