Q: What metric-dimension combination is not valid?
A) Total Events / User Type
B) Sessions / Source
C) Avg. Time on Page / Device Category
D) Sessions / Bounce rate
Correct Answer is D) Sessions / Bounce rate.
In Google Analytics, every website visitor has a corresponding source and medium. For example, google/organic, example.com/referral, and newsletter1/email. Source and Medium are default source dimensions in Google Analytics.
Tip: Don’t confuse sources with mediums as it often happens. Source is the origin of your traffic. While Medium is a category of a traffic source.
Learn more on the official Google support website.