
Passage: The 12th International Congress of Logic, Methodology and Philosophy of Science was held in Spain, and at least one of Prof. Hacker, Prof. Maas and Prof. Reger attended the conference. Known: (1) Those who sign up for the conference must submit an English academic paper, and the invitation letter will be issued after expert review. (2) If Prof. Hacker attends this conference, then Prof. Maas must attend. (3) Prof. Reger submitted a German academic paper to the conference.
Question: Based on the above, which of the followings must be true?
A. A.Prof. Hacker attended the conference.
B. B.Prof. Maas attended the conference.
C. C.Prof. Reger attended the conference.
D. D.Both Prof. Hacker and Prof. Maas attended the conference.
Answer: