The correct answer is C. label.
A label is a piece of text that identifies or describes something. It is usually placed on an object or container to provide information about it. The most important property of a label is its text, which should be clear, concise, and easy to understand. The text should also be relevant to the object or container it is attached to.
The other options are not as important as the text of a label. The background of a label is usually used to make the text stand out. The caption of a label is a brief description of the object or container it is attached to. The text of a label is more important than the background or caption because it provides the most information about the object or container.