The plural for wash is wash, as in the following sentence:
Jenny brought in the wash, which was left outside.
However, it might have to be washes in cases like this:
Nicholas signed up to do seven car washes on Saturday.
Bridges is the plural form of bridge.
Radios
"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.
There is no plural form of pupae. Pupae is the plural form of pupa.
The plural of bathtub is bathtubs.
The plural of bathtub is bathtubs.
soap scum sticks to the side of the bathtub witch causes bathtub rings to form.
Yes, it is very common for a vortex to form in a bathtub as it drains.
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."
Radios
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.