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: 'while looking in the rear view mirror this person saw their dog with his head out the window'. Reverse all words of length '4' in the given sentence.

while looking in the raer weiv mirror siht person saw their dog htiw his daeh out the window