The word 'which' has no plural form.
The word 'which' is a pronoun when not followed by a noun:
Interrogative pronoun: Which is the best cheese for this dish?
Relative pronoun: I can't decide which is best.
The word 'which' is a determiner when followed by a noun:
Which movie would you like to see?
I can't decide which movie.
Singular ; this and that Plural ; these and those
The plural for the noun loss is losses; the plural possessive is losses'.
plural verb - were plural subject - boys The boys were hungry
The plural is a normal S plural, associates.
The plural is a normal S plural, races.
Singular ; this and that Plural ; these and those
The plural of rose is roses. The plural possessive is roses'.
The plural of 'bunch' is bunches.The plural of 'ant' is ants.The plural of 'batch' is batches.The plural of 'day' is days.The plural of 'chimney' is chimneys.The plural of 'tomato' is tomatoes.The plural of 'umbrella' is umbrellas.The plural of 'donkey' is donkeys.The plural of 'sky' is skies.The plural of 'foot' is feet.The plural of 'show' is shows.
applied is does not have a plural but is apply it does have a plural.
The plural is a regular plural, attics.
The plural for the noun loss is losses; the plural possessive is losses'.
pluralsThe word plurals is the plural of plural. As in: I answered the question about plurals to the person who didn't know that the plural of plural is plurals.
pluralsThe word plurals is the plural of plural. As in: I answered the question about plurals to the person who didn't know that the plural of plural is plurals.
Singular ' He/She is Plural 'They are NB Notice they change of verb. NNB 'They is' is NOT correct English.
There is no plural for which
is are the plural of is
Yarn is an irregular plural so plural for yarn is yarn. It can be singular or plural.