To answer this question, you need to understand the concept of intellectual property and copyright.
Option A) proprietary - This option is incorrect. Proprietary refers to something that is owned and controlled by a specific individual or organization. It implies that the technology is protected by copyright and is not available to everyone.
Option B) open - This option is incorrect. Open refers to something that is freely available and accessible to everyone, without any restrictions. It does not imply that the technology is no longer protected by copyright.
Option C) experimental - This option is incorrect. Experimental refers to something that is being tested or tried out, often with the purpose of gathering data or exploring new ideas. It does not imply that the technology is no longer protected by copyright.
Option D) in the public domain - This option is correct. When something is in the public domain, it means that it is no longer protected by copyright and is available for public use. This includes technology, creative works, and other intellectual property that can be freely used, modified, and distributed by anyone.
The correct answer is D) in the public domain. This option is correct because it accurately describes technology that is no longer protected by copyright and is available to everyone.