Culture is a combination of material equipment and all kinds of knowledge. People use equipment and knowledge to survive. For some purpose, people sometimes change the culture. If a person throws away a certain tool to get a new tool, it is because he Believe that the new tool is more applicable. This process of change must be a kind of synthesis, that is, his past experience, his understanding of the current situation and his expectations of future results. Past experience is not always a true portrayal of past events. Because of past events, the choices made through memory have changed; the current situation is not always accurately understood, because the degree to which it attracts attention is often affected by stakes; future results will not always be as human As expected, because it is the product of many forces other than hope and effort, the new tool may also prove to be unfit for human purposes. If the new tool turns out to be unsuitable for a purpose, which of the following is not explicitly mentioned by the author? ['The tools chosen are not suitable for productivity.', 'The historical experience on which it is based may be wrong.', 'c. Understanding of the current objective situation may be incomplete.', 'Unexpected new situation in the development process.']