Final answer:
The word 'obsolete' in the given sentence can be understood through the List context clue technique, which lists outdated technologies, implying that 'obsolete' means no longer in use.
Step-by-step explanation:
To determine the meaning of the word obsolete in the given sentence, you would use the List context clue. This clue type provides examples to help you infer the meaning of the word. In the sentence, 'Many items that were once quite useful are now considered obsolete: the telegraph, cassette players, and fax machines,' the items listed (telegraph, cassette players, fax machines) are all known to be outdated technologies, which are no longer in common use. This allows you to infer that obsolete means something that is no longer in use or has been replaced by newer technology.