The song "Happy Birthday to You" was originally written in 1893 as "Good Morning to All." The tune was the same, but the lyrics were different. Mildred and Patty Hill, who wrote the song, then changed the words and had the song published by Clayton F. Summy Company. Summy filed for a copyright in 1935 for "Happy Birthday to You." Warner Music claimed it acquired the copyright to the song in 1988. However, the Association for Childhood Educational International, a nonprofit group co-founded by Patty Hill that has collected a great deal of the $2 million per year in royalties coming in over the years, claims that if Warner is not the copyright holder, then it is. What do you need to know to determine if the copyright is still valid? a. how the Association got its interest b. whether the song has become generic c. when the last Hill sister died d. whether Warner paid for the copyright