50. According to the passage, which of the following statements is true? (A) Tai Chi has again attracted Chinese people’s attention since 1990’s. (B) Tai Chi is strongly recommended as the sole treatment to cardiovascular disease. (C) Tai Chi, a non-vigorous exercise, can only be practiced between 30 minutes to an hour every day. (D) Tai Chi, though an exercise of low-to-moderate intensity, is helpful to cardiovascular disease patients.