Which tag can be semantically empty to maintain table structure?

The correct choice is TD because, in the context of HTML tables, a table data cell (TD) can be semantically empty while still maintaining the overall structure of the table. When a TD element is empty, it does not disrupt the grid layout of the table, allowing for the intended design and data organization to remain intact.

An empty TD is often used in scenarios where spacing or visual structure is required without the need to display content. For example, this can help align other cells properly or manage row and column designs, which is crucial for accessibility and usability.

On the other hand, elements like LI, Div, and Span have different roles and are not typically used to structure tables. While they can be styled or manipulated in various ways, their inclusion as table cell elements is not semantically correct, and making them empty does not help in representing the tabular data appropriately as TD does. This distinction is vital for ensuring accurate and accessible table representation in HTML documents.