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: 'the dog lies on the bed as the cat is looking out of the window'. Reverse all words of length '3' in the given sentence.

eht god lies on eht deb as eht tac is looking tuo of eht window