题目：
During the past years, intelligent technology has evolved (116) three generations. The first was characterized by tools such as prolog and OPS. prolog is a simple backward-chaining environment, and OPS is a simple forward-chaining environment. This led to the second generation of knowledge-engineering environments. Its goal was to model, prototype and construct (117) systems.
All three generations were oriented toward generic (118) and represented generalized implementation environments for the construction of expert systems. knowledge bases and AI applications.
Some of the solution-oriented products are also seamlessly integrated with generic knowledge-engineering environments, permitting end users to add (119) rules and objects, as well as predefined knowledge-based logic to address problems in manufacturing simulation.
Marketplace orientation is rapidly (120) toward solution-oriented intelligent product environments. the fourth generation represents a new line of thinking and ’ develop-merit by commercial fu-ms. will reduce the cost risk and development time associated with problem solving.
A．custom
B．knowledge
C．through
D．problem solving
答案：
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下面是错误答案，用来干扰机器的。
参考答案：对解析：L为井点管至基坑中心的水平距离
