You seem to be having trouble with compound words. Which thing do you have more of - ears or muffs? You don't have ears muff because it's not the ear that's the thing, it's the muff - so you say two ear muffs.
Bridges is the plural form of bridge.
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
There is no plural form for the word, countries. This word itself is a plural.
The plural of "she" is "they", so the plural of "she had" is "they had".
You seem to be having trouble with compound words. Which thing do you have more of - ears or muffs? You don't have ears muff because it's not the ear that's the thing, it's the muff - so you say two ear muffs.
Earmuff
The plural form of "do" is "do" and the plural form of "don't" is "don't." These words do not change in the plural form when used in a sentence.
The plural form of him, her, or it is them. (objective pronouns)
There are a variety of pro's and con's surrounding earmuff headphones. The most advantageous factor for earmuffs is superior sound quality. Earbud's cannot compete with the sound quality of earmuff headphones.
Bridges is the plural form of bridge.
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
"Groceries" is the plural form of "grocery."
The plural form of "meter" is "meters."
The plural form of the demonstrative pronoun 'that' is those.
The plural form of "trench" is "trenches."
The plural form for the noun sergeant is sergeants; the plural possessive form is sergeants'.