As the European powers grew more industrialized, their colonies became very important as sources of A)slave labor. B)raw materials. C)new inventions. D)military prestige.

B) Raw materials; As stated, European powers did indeed grow more industrialized, therefore they needed more raw materials. The North provided lumber, spent time whaling, etc.. The South spent time growing cash crops such as rice, cotton, and indigo. 

Raw materials is the answer your looking for i just took the testXD LUL