A non-subjective issue has generally accepted criteria that can be used to judge it while a subjective issue does not.
asaa
Pitch
what were two key differences between the north's economy and the south's economy?
The key religious differences between the European nations that explored the Americas is the same as the rest of the world. Some are Muslims, Christians and so on.
none
piano has more keys
The key religious differences between the European nations that explored the Americas is the same as the rest of the world. Some are Muslims, Christians and so on.
The key difference is that while Giotto was a painter, Machiavelli was a writer.
bark run
india-delta-ten-tango......
The conventions
There are many differences between Wiki and Google. Google is an engine that finds information from millions of websites based on key words. Wiki finds information based on key words, but the only information they find is from articles from Wikipedia.