Final answer:
A filter has multiple applications; it is used in photography to transmit specific wavelengths of light, in signal processing to eliminate unwanted frequencies, and as a function in spreadsheets to hide rows that don't meet specific criteria.
Step-by-step explanation:
Filters come in various forms and serve multiple purposes across different fields. For instance, a blue filter in photography typically absorbs all visible light except for the blue wavelengths it's designed to transmit, creating an effect where only blue light is seen. In contrast, the suggestion that a blue filter absorbs blue light is inaccurate; such a filter would reflect or transmit blue light instead.
In the context of electronics and signal processing, a filter can indeed eliminate unwanted frequencies from a signal. This helps in cleaning up audio signals, radio frequencies, and other types of data transmission. For example, audio engineers use filters to remove hissing noises or to fine-tune the sound quality of recordings.
Regarding spreadsheets, the term filter refers to a function or feature that allows users to conceal non-relevant rows based on certain criteria, streamlining the viewing process. While sorting, such as arranging data in alphabetical order, is a related functionality, it is distinct from filtering.
Therefore, from the given options, the correct descriptions of a filter would be: B. A filter can eliminate unwanted frequencies in a signal, and D. A filter is a type of spreadsheet function.