People in the middle ages were members of what three classes? merchants noblemen serfs clergy villagers

Clergy, noblemen, serfs.

In the Middle Ages, there was a definite structure in society. You were born into a class of people and generally stayed in that class your entire life. After the rank of King, there hierarchy was  the nobles, the clergy and then serfs.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.