Which sentence from the passage expresses an opinion rather than a fact?

Question

"The feudal system relied on serf labor to survive"

"Relationships between each level of society relied on the exchange of loyalty and services"

"In addition to the labor and taxes that the serfs provided to the lords, serfs also gave their lords the extra harvest to pass along to their landlords"

"Although serfs provided the manor with an important source of money and labor, it is important to remember that their lives were full of hardship

Answer 1

And you think … ?

Answer 2

I thought it was B but I was wrong

Answer 3

So this is my second attempt

Answer 4

So go through the choices and ask yourself if each one can be proven or not. Obviously, you can now skip B.

"The feudal system relied on serf labor to survive" <~~Can this be proven?
Etc.

Answer 5

So are you saying that the answer is A