Is there any way feudal lords could have worked their lands without using serfs?

Serfs. are needed as The feudal lords did not work their lands,  In western Europe the whole system of serfdom although having its origins in the late Roman Empire, was very largely the rule of an alien aristocracy over a native population. The invaders were not farmers, they were warriors, and in later centuries at least until the agricultural revolution they showed little interest in the actual management of their estates, largely leaving that to Reeves or in modern terms estate managers. 
For a medieval feudal lord or a Russian aristocrat until the 19th century, his serfs were as much his property as his horse and hounds. Their labour, skills and occasionally their use as auxilliary soldiers was the source of his wealth and power. The extent of his lands the measure of his importance. It would have been almost impossible for him to think in modern terms of allowing his serfs to become free, even though in the late middle-ages they largely became share-croppers.
hope this helps 

The correct answer is c