Crescendos
The plural of crescendo is crescendos. As in "the crescendos in these musical pieces are stunning". I'm not convinced adding 's' make crescendo plural! In English, with borrowed words, we often simply add 's' to make a plural like: 'piano/pianos'. Whereas normally, when a word ends in 'o' we add 'es' like 'potato/potatoes'. There is no definite rule. With other Italian words, we often follow the Italian rule by changing the 'o' to 'i' as in 'Paparazzi/Paparazzo', 'graffiti/graffito'. Therefore, I'd say the plural of crescendo is crescendi. As it is a borrowed word, I'd say it could be acceptable to use 'crescendos', (it is now acceptable to use 'stadiums' rather than 'stadia' to make stadium plural. Or referendums/referenda etc) but a purist wouldn't.
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 "was" is "were."
The plural form of "I" is "we."
A crescendo does not have a theme. A crescendo means that you must gradually get louder.
"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.
The plural form of the demonstrative pronoun 'that' is those.