Choose the sentence in which the Phrasal Verb use of "Polish off' has been used correctly.

The servant polished off the shoes of all inmates. My brother polished off all the cake that was in the box. The Speaker polished off his speech beautifully. All the students polished off their text books completely.

My brother polished off all the cake that was in the box.

The sentence in which the Phrasal Verb "Polish off" has been used correctly is: My brother polished off all the cake that was in the box. To "polish off" something means to eat or drink it quickly and completely. This definition aligns perfectly with the sentence about the cake.