The word do is a verb. Verbs are neither plural nor singular.
english plural - agenda
The plural of stimulus is stimuli.
English plural: tourist > tourists Foreign plural: touriste > touristes
Winned is not an English word so there is no English plural
The plural of syllabus is syllabi.
The English plural is symposiums. The Latin plural symposia is also used.
The plural of "English-speaking country" is "English-speaking countries."
Yes, the plural of "is" is "are" in English.
English
The less-used English plural is curriculums. The more widely-used Latin plural is curricula.
The Latin plural is bursae. The English plural is bursas.
The singular form is bacterium; the plural form is bacteria.