In the conversation, B answered A's question indirectly to perform politely. A's painting may be not very well but B's answer may show that he doesn't know how to appreciate it and B uses this way to save A's face. In Leech's opinion, indirect speech act are to be polite. Leech believes the main reason why people violate Cooperative Principle intently is the consideration of politeness. Leech proposed the Politeness Principle which is formulated in a general way from two aspects:

1) to minimize the expression of impolite beliefs;
2) to maximize the expression of polite beliefs.

The Politeness Principle encompasses six maxims: Tact maxim, Generosity maxim, Approbation maxim, Modesty maxim, Agreement maxim and Sympathy maxim.

Politeness Principle is an important conversational principle. Politeness is usually known as a kind of tactics which is used to do something, like maintaining or promote the harmonious relationship with others. In communication, the best way to save one's face may be of polite utterances. To be polite, people often flout conversational maxims to express themselves indirectly.

本题考查礼貌原则。 首先解释礼貌原则的含义以及遵守礼貌原则的原因， 然后结合所给对话分析礼貌原则的运用。