Ali: I am doing a science project about inventions. I need to find the inventor of the light bulb.
Zeynep: That is Thomas Edison. He invented it in 1879.
Ali: Thanks. I also need to know about a discovery in medicine.
Zeynep: You should research Alexander Fleming. He discovered penicillin in 1928.
Ali: Great! Now I have enough information for my project.
Which of the following questions does **NOT** have an answer in the conversation?
A)Who invented the light bulb?
B)When was penicillin discovered?
C)How did Alexander Fleming discover penicillin?
D)What is Ali's project about?