Which of the following statements about Buddhism are true?

1. Theravada Buddhism is primarily practiced in China and Japan and places greater emphasis on Buddha's teachings and the monastic community.
2. Mahayana Buddhism, practiced primarily in Sri Lanka and Southeast Asia, focuses more on the celestial Buddhas and Bodhisattvas.
3. Skandhas, in Buddhism, refers to the five components that sum up an individual's mental and physical existence.
4. The state of Nirvana in Buddhism is the attainable state of pure existence, free from suffering, desire, and the cycle of rebirth.