When does a consistency point (CP) flush to disk occur?

When does a consistency point (CP) flush to disk occur? (Choose two.)

A.
When NVRAM is full

B.
When NVRAM is 50% full

C.
Every 20 seconds

D.
Every 10 seconds

Explanation:
http://www.slideshare.net/taotao1240/wafl-overview (slide 6)