Which event marked the beginning of the Middle Ages?

A. the collapse of the Roman Empire
B. the search for new trade routes
C. the Crusades
D. the Renaissance

The answer is Fall of Rome but these words doesn't exist in the options. So is the answer A?

Yes, even though "collapse" is not quite the right word. It certainly didn't happen in a day or even a year!

And, scholars debate the issues..

https://en.wikipedia.org/wiki/Timeline_of_the_Middle_Ages

Yes, you are correct. The event that marked the beginning of the Middle Ages is the collapse of the Roman Empire. Although the phrase "Fall of Rome" is not explicitly mentioned in the options, option A, which states "the collapse of the Roman Empire," corresponds to that event and is the correct answer in this case.