How did nationalism contribute to the decline of the habsburg empire?

The Habsburg Empire was composed of many different people groups.  As nationalism became a strong force during the 19th century, there was pressure by individual national groups within the empire to have sovereignty over their own affairs.

In the 19th century, when nationalism began to rise up as a powerful political force, it had the tendency either to unite or divide, depending on circumstances.  In areas like the Italian peninsula or the German states, there was a uniting power to the aspirations of nationalism, bringing people together into a unified Italy and a unified Germany.  But elsewhere, in areas like the Austrian Habsburg Empire or the Ottoman Empire, nationalism tended to divide those territories.  People groups identifying themselves according to a common "national" or ethnic identity sought to break into their own independent nation-states.

the answer is option a.