One way of looking at "barabrians" is

Barbarian is defined as a person who is savage and crude. A cannibal is an example of a barbarian. and barbaric” is most commonly used to describe an act that is either brutal or cruel to the point of savagery or primitive and uncivilized (or all of the above) while a “barbarian” is a person who commits such acts or displays such characteristics

the correct labels are as follows:

a: yellow river

b: himalayan mountains

c: north china plain

d: taklimakan desert