Three of the following were obligations owed by a vassal to his lord. Which was NOT?

a. tithe

b. scutage

c. relief

d. ransom

What wasn't required from the vassal to give his lord was d - ransom.

The vassal didn't need to pay any ransom to his lord because ransom was usually paid when the lord or anyone of noble birth was captured. When this happened he was able to pay his way out and be freed through ransom.