Categorize the type of sampling (simple random, stratified, systematic, cluster, or convenience) used in each of the following situations.
A) To conduct a preelection opinion poll on a proposed amendment to the state constitution, a random sample of 10 telephone prefixes (first three digits of the phone number) was selected, and all households from the phone prefixes selected were called.
B) To conduct a study on depression among the elderly, a sample of 30 patients in one nursing home was used.
C) To maintain quality control in a brewery, every 20th bottle of beer coming off the production line was opened and tested.
D) Subscribers to the magazine Sound Alive were assigned numbers. Then a sample of 30 subscribers was selected by using a random-number table. The subscribers in the sample were invited to rate new compact disc players for selecting the songs in the playlist.