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.

Example Input: Sentence: 'a couple of elephants that are in some water'. Reverse all words of length '6' in the given sentence.
Example Output: a elpuoc of elephants that are in some water

Example Input: Sentence: 'a very large truck with people in back on a city street'. Reverse all words of length '6' in the given sentence.
Example Output: a very large truck with elpoep in back on a city teerts

Example Input: Sentence: 'a man that is sitting on a park bench'. Reverse all words of length '7' in the given sentence.
Example Output:
a man that is gnittis on a park bench