A Mute Mental Patient Is First Given a Token Each

A mute mental patient is first given a token each time he or she says a word. Next, tokens are given for speaking a complete sentence. Later, the patient is gradually required to speak more often, then to answer questions, and eventually to carry on a short conversation in order to receive tokens. This gradual improvement of the patient's communication skills is an example of

A) shaping.
B) reciprocal inhibition.
C) classical conditioning.
D) systematic desensitization.