hello guys i came across a question that is:
Mammoth Cave in Kentuck,Whic is ...... cave in the world,has 345 miles of subterranean passageways.
i reduced the answers to the longest and longest.But ı dont know what is the difference between them
A cave is a "countable noun", so
Mammoth Cave in Kentucky, which is the longest cave in the world, has 345 miles of subterranean passageways.
Please see the Oxford Dictionary page about Countable and uncountable nouns
I can't think of any contexts in which we would use a superlative like longest without "the" or another determiner like "my" (except in Headlinese, where articles are usually omitted).