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 is a group of people standing on the beach'. Reverse all words of length '8' in the given sentence.
Example Output: there is a group of people gnidnats on the beach

Example Input: Sentence: 'reflection of window on mirror in dark bathroom'. Reverse all words of length '10' in the given sentence.
Example Output: noitcelfer of window on mirror in dark bathroom

Example Input: Sentence: 'a group of people that are sitting in a boat'. Reverse all words of length '6' in the given sentence.
Example Output:
a group of elpoep that are sitting in a boat