向滴有紫色石蕊溶液的水中通入二氧化碳，可见现象为                     ，有关反应的化学方程式为                     ；将上述得到的溶液加热煮沸，可见现象为                      ，有关反应的化学方程式为                     。

Artificial intelligence (AI) ,an interdisciplinary field, is usually regarded as a branch of computer science, dealing with models and systems for the performance of functions generally associated with human intelligence, such as (71) and learning.

In AI, knowledge-based system is an information (72) system that provides for solving problems in a particular domain or application area by drawing inferences from a knowledge base. Moreover, some knowledge-based systems have learning capabilities.

Expert system (ES) indicates the knowledge-based system that provides for solving problems in a particular domain or application area by drawing inferences from a knowledge base developed from human (73) . Some expert systems are able to (74) their knowledge base and develop new inference rules based on their experience with previous problems. The term "expert system" is sometimes used (75) with "knowledge-based system", but should be taken to emphasize expert knowledge.

（74）处填（）。

A．renew

B．improve

C．upgrade

D．amend