The Four Masters of Regular Script are the collective name for the four calligraphers who are famous for their regular script in the history of calligraphy, also known as the Four Great Regular Scripts. They respectively refer to: Ouyang Xun (European style) of the Tang Dynasty, Yan Zhenqing (European style) of the Tang Dynasty Yan Ti), Liu Gongquan of the Tang Dynasty (Liu Ti), Zhao Mengfu of the Yuan Dynasty (Zhao Ti).
So choose C.