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: 'there are many animals standing on the top of this mountain'. Reverse all words of length '4' in the given sentence.
Example Output: there are ynam animals standing on the top of siht mountain

Example Input: Sentence: 'a gray tiger cat sitting on top of a chair'. Reverse all words of length '3' in the given sentence.
Example Output: a gray tiger tac sitting on pot of a chair

Example Input: Sentence: 'flowers are on an office desk with a sign that states visitors must sign in'. Reverse all words of length '8' in the given sentence.
Example Output:
flowers are on an office desk with a sign that states srotisiv must sign in