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 black dog is on grass holding an orange frisbee in his mouth'. Reverse all words of length '3' in the given sentence.

a black god is on grass holding an orange frisbee in sih mouth