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 giraffes standing in front of a metal fence'. Reverse all words of length '8' in the given sentence.
Example Output: a couple of seffarig gnidnats in front of a metal fence

Example Input: Sentence: 'a man being towed behind a boat on a board'. Reverse all words of length '4' in the given sentence.
Example Output: a man being towed behind a taob on a board

Example Input: Sentence: 'a couple of people riding skis on top of snow covered ground'. Reverse all words of length '4' in the given sentence.
Example Output:
a couple of people riding siks on top of wons covered ground