Under Maria Theresa, Austria's greatest enemy was

a. Bohemia.

b. Hungary.

c. Prussia.

d. the Ottoman Empire.

C Prussia

There were three wars between Austria of Habsburgs (and their changing allies) and Hohenzollern's Prussia for control of Silesia, which resulted in most of Silesia (as well as land of Kłodzko) were within the borders of the Prussia, and with them since 1871 united by the Hohenzollern German Empire. During reign of Maria Therese Silesia had predominantly Polish and Czech speaking population