Knowledge points Tang Dynasty calligraphy.
Answer B.
Yan refers to Yan Zhenqing and Liu refers to Liu Gongquan, both of whom are famous calligraphers in the Tang Dynasty. Yan Zhenqing's calligraphy is clumsy and vigorous. Liu Gongquan's calligraphy has sharp edges and corners, and is famous for strengthening bones. "Yan Gu" means that their style is as strong as bones and muscles.