If the subject matter of your article is appropriate to several groups, you can specify them all when posting. Do not put spaces around the commas. Read the manual or try the help command for your newsreader to determine the exact command for cancelling an article. Some newsreaders don't show read articles unless you search for them, so it may first be necessary to locate the article you wish to cancel. Test articles are prime candidates for cancellation.
Most newsreaders provide a command for listing available groups.
The lists of newsgroups in the CWIS are fairly complete, and can show you what is available elsewhere. This varies from machine to machine. There are several newsreaders available for the various kinds of personal computers. These are not supported by Computing and Communications, but are available via anonymous ftp archives on the Internet. There are two aspects to this.