Suzanne supervises telemarketers who sell two different services, services Z and Y. In the past, the two services have had the same level of success. However, last year, Suzanne changed the telemarketing tactics for selling service Z for a trial period. At the end of the year, Suzanne found that service z was selling far better than service y. Which of the following is definitely true? A) The tactics used to sell service Z were changed last year. B) The tactics used to sell service Y remained the same last year. C) The change in telemarketing tactics for service Z resulted in an increase in sales for that service. D) Both A and B are true. E) Both A and C are true.