The plural form for the noun guard is guards.
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
The plural form of "is" is "are."
The plural form of "was" is "were."
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.
Guard-houses.
Guards
Singular: guardPlural: guards
The plural of guard is guards. As in "the dog closely guards the cookie she just stole".
doctors' guards' jockeys' milkmen's umpires'
house
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."
Singular ; 'I' ( NB ALWAYS a CAPITAL letter). Plural ; 'we'
The plural form of "was" is "were."