Answer :
Sentence fragment is defined as the set of words that look like sentences but actually they are not.For a sentence there should be a absolute clause.
therefore,
first and second option have absolute clause while third one is sentence fragment.
hence the right option is C) When we stopped by the garden.
therefore,
first and second option have absolute clause while third one is sentence fragment.
hence the right option is C) When we stopped by the garden.