Definition: In this task, you need to reverse all words of a given length in the sentence. The number of letters in a word determine its length. For example, the length of the word "apple" is 5.
Input: Sentence: 'a cat lying on a mat on the floor beside a pair of shoes'. Reverse all words of length '3' in the given sentence.

a tac lying on a tam on eht floor beside a pair of shoes