Scientists have invented ___ intelligent computer systems capable of answering questions posed in natural language.(Artificial)

The correct answer is "artificial." The phrase "artificial intelligent computer systems" is a commonly used expression referring to machines that can perform tasks that typically require human intelligence, such as understanding and processing natural language.

In this context, "artificial" describes the nature of the intelligence being referred to. The term "artificial intelligence" (AI) is widely recognized in the field of computer science and technology, and it implies that the intelligence exhibited by these systems is not natural but created through programming and algorithms.

Therefore, the completed sentence should read: "Scientists have invented artificial intelligent computer systems capable of answering questions posed in natural language." This indicates that these systems use artificial intelligence techniques to understand and respond to queries made by users in the way that humans naturally communicate.