The word 'broad' is an adjective. Adjectives don't have plural forms, adjectives have degrees:
The plural form for the noun arch is arches.
The noun 'fungi' is the plural form of the noun 'fungus'.
The plural form of inadvertence is inadvertences.
The plural form of itch is itches.
The plural of verandah is verandahs.
The word 'broad' is an adjective. Adjectives don't have plural forms, adjectives have degrees:broad (positive)broader (comparative)broadest (superlative)
The noun spectacles is a shortened form for the term 'pair of spectacles'. The plural form is two pairs of spectacles.The nouns spectacles belongs to a group of nouns that are a shortened form for 'a pair of', for example:binocularsglassespantsscissorsshearsshortsspectaclestongstrouserstweezersAll of these nouns are made plural by changing 'a pair of...' to 'pairs of...'.
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "I" is "we."
The plural form of "was" is "were."
The comparative form of "broad" is "broader."
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.