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 giraffe is is facing the camera while the rear of another giraffe appears in the background'. Reverse all words of length '3' in the given sentence.

a giraffe is is facing eht camera while eht rear of another giraffe appears in eht background