In communication one may shift from formal English to informal English or from standard English to non-standard English. This is known as ______.

A．The lions were on the brink of extinction.
B．They were suffering from a fatal disease.
C．They allowed him to see their vitality and charm at close quarters.
D．Mother lion and her cub shared a deer.

A．They are physically weaker than the African lions.
B．They are small in size.
C．They do not have enough to eat.
D．They have descended from a dozen or so ancestors.