低回声是什么意思

This is a maintenance category, used for maintenance of the Wikipedia project. It is not part of the encyclopedia and contains non-article pages, or groups articles by status rather than subject. Do not include this category in content categories.

This is a tracking category. It builds and maintains a list of pages primarily for the sake of the list itself. They are not part of the encyclopedia's categorization scheme.

• This category is hidden on its member pages—unless the corresponding user preference (Appearance → Show hidden categories) is set.
• These categories can be used to track, build and organize lists of pages needing "attention en masse" (for example, pages using deprecated syntax), or that may need to be edited at someone's earliest convenience.
• These categories also serve to aggregate members of several lists or sub-categories into a larger, more efficient list (discriminated by classifications).