Although data is the plural of Latin datum, it is commonly used in English as singular.
In formal academic language, however, data is still often plural:
The data are inconclusive.
Criteria is the plural of criterion:
The sole criterion in the selection process was …
Many criteria were used in the selection process.
Phenomena is the plural of phenomenon:
This phenomenon can be seen in …
Several different phenomena can be observed …
Media is the plural of medium:
The internet is a new and exciting medium.
The media are often blamed for society’s ills.
Bacteria is the plural of bacterium:
A single bacterium is too small to be seen with the naked eye.
While some bacteria are harmful, others are beneficial.
Strata is the plural of stratum:
Each stratum represents a different period.
Sequences of sedimentary strata