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: 'man stands on elephants leg while bathing the elephant in the river'. Reverse all words of length '8' in the given sentence.

man stands on elephants leg while bathing the tnahpele in the river