A．sign language was not extensively used even by deaf people
B．sign language was too artificial to be widely accepted
C．a language should be easy to use and understand
D．a language could only exist in the form of speech sounds

A．sign language is as efficient as any other language
B．sign language is derived from natural language
C．language is a system of meaningful codes
D．language is a product of the brain

A．孔子告诫：“君子耻其言而过其行。”
B．孔子告诫：“君子喻于义，小人喻于利。”
C．孟子告诫：“不耻不若人。何若人有。”
D．孟子告诫：“人不可以无耻。无耻之耻。无耻矣。”