In the text of a research article, if a reference is cited by writing the author name followed by et al., which among the following could represent the number of authors involved in the cited study?

The abbreviation et al. is used for a work with three or more authors.

It replaces the additional names after the first author in the text.

A study with three authors can be cited with et al.

A study with four authors is likewise cited with et al.

A single author is always named in full, so et al. never applies.

Two authors are both named and joined, without et al.