The most powerful Catholic ruling family in the 1600s was the:

a. Tudors

b. Hapsburgs

c. Hohenzollerns

d. Bourbons

I think the answer is A

The Habsburgs, 100%. The Tudors weren't Catholic, and famously so. The Hohenzollerns and Bourbons never came close the the Holy Roman Empire in power at its pique. The Hohenzollerns were later as well, although I confess I am not quite as learned on their history. Had the Tudors been Catholic, it might be a contest, as Elizabethan England was certainly a height of the British Empire.