http://www.uottawa.ca/academic/arts/writcent/hypergrammar/subjpred.html
Read about subjects here; then let us know what you think and why. Someone here will be happy to let you know if you're right.
"One story links this day to an old Roman festival." What is the subject
2 answers
Or, ask yourself this question: WHAT is this talking about? That should give you the subject.