Aquarium is singular. The strict plural is aquaria, though modern usage would often be aquariums.
practitioner is singular (plural practitioners)sofa is singular (plural sofas)satellite is singular (plural satellites)clips is plural (singular clip)dentist is singular (plural dentists)dollars is plural (singular dollar)article is singular (plural articles)magazines is plural (singular magazine)laminator is singular (laminators is plural)radios is plural (singular radio)
singular and plural
Singular: book / Plural: books Singular: cat / Plural: cats Singular: child / Plural: children Singular: foot / Plural: feet
Are is plural. "Is" is singular. For example, "There is a glove on the chair". That is singular. "There are gloves on the chair". That is plural.
"Has" is singular, e.g. He has, she has. "Have" is plural, e.g. They have, we have. The exception is "I" - e.g. I have.
In the example sentence, "Which fish in the aquarium swims the fastest?", the noun "fish" may be singular or plural. The noun "aquarium" is singular.The noun "fish" is an uncountable (mass) noun as a word for a food substance, but can be used as a count noun (fish, fishes) as a word for the creature (creatures).Example: How many fish are in your aquarium?Or: How many fishes are in your aquarium? (both sentences are correct)
The word team is singular; the plural form is teams.
'These' is the plural form of 'this'.
Who may be singular or plural.
This is singular. These is the plural form.
These is plural, this is singular
"Notebook" is singular. The plural form is "notebooks."