Which Unity version is used for "Unity Certified Associate" exam?

Nested prefabs are present in Unity 2018.3 but not before that. So answer to some older questions would not be valid with newer versions of Unity.

Also there are some visual changes to the way gameObjects and prefabs are rendered in Unity among different versions.

Some of the questions include screenshots of gameObjects and asking students to differentiate among gameObjects and prefabs just based on their visual appearance. I afraid that my students get confused over them (although I'm going to explain it to them).