Plural or Singular Nouns?

Front

A group of boys

Back

Singular

Answer explanation

the main subject here is "A group" which suggests ONE group.

Front

Feet

Back

Plural

Answer explanation

Feet is the plural noun for 'foot'

Front

Tooth

Back

Singular

Answer explanation

Tooth is the singular for 'teeth'

Front

A pair of shoes

Back

Singular

Answer explanation

'A pair' suggests ONE pair --> singular

Front

One of the boys

Back

singular

Answer explanation

the subject here is 'ONE' of the boys. It means that the focus here is only ONE of the many boys -> singular