The correct answer is D. no article.
The sentence “Please close the window. It’s cold in here” is a command. In commands, we do not use articles. For example, we would not say “Please close a window” or “Please close the windows.” We would simply say “Please close the window.”
The reason we do not use articles in commands is because we are not referring to a specific window. We are simply telling the person to close any window that is open.
If we were to refer to a specific window, we would use an article. For example, if we were talking about a window that was open in the living room, we would say “Please close the living room window.”
In this case, we are referring to a specific window, so we need to use an article.
However, in the original sentence, we are not referring to a specific window. We are simply telling the person to close any window that is open. Therefore, we do not need to use an article.