Regarding Confucianism, which of the following statement is correct?

A、The most important concept of Confucianism is Ren(仁).;
B、Confucius regarded Ren(仁) as the cornerstone of his whole system of ethics.;
C、Classical Confucian philosophy is one of the three most important schools of Chinese philosophy.;
D、The Platform Sutra is one of the canonical works of Classical Confucian philosophy.