#EngTrivia: Confusing singular/plural word

English plurals are usually easy to form. We can add -s to the end of the singular word, e.g.: chair (singular) or two chairs (plural). But, like almost all of the rules in English grammar, there are exceptions for the plural form of some nouns. Here is a list of the confusing singular/plural words.

Criterion (singular) – criteria (plural). Meaning: a rule or principal used in evaluation.
- Example:
  - “One criterion for grading this essay will be announced.”
  - “What were the criteria used to choose the winner?”
Phenomenon (singular) – phenomena (plural). Meaning: an observable fact or event.
- Example:
  - “Star Wars eventually became a cultural phenomenon.”
  - “Lightning and earthquakes are natural phenomena.”
Datum (singular) – Data (plural). Meaning: a single piece of information
- Example:
  - “The datum shows little without the rest of the statistics.”
  - “The data were collected over a period of three months.”
Stratum (singular) – strata (plural). Meaning: a level or class to which people are assigned according to their social status, education, or income.
- Example:
  - “Discrimination exist in every stratum of society.”
  - “Different social strata are most likely crashing into each other.”
Bacterium (singular) – bacteria (plural). Meaning: a type of unicellular microorganism that are important to human because of their chemical activities but some of its type often cause disease.
- Example:
  - “Every bacterium is prokaryotic.”
  - “Tetanus is a serious illness caused by Clostridium tetani bacteria.”