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 group of sheep graze in a grassy field'. Reverse all words of length '2' in the given sentence.
Example Output: a group fo sheep graze ni a grassy field

Example Input: Sentence: 'a man watches two giraffes eating from a box'. Reverse all words of length '4' in the given sentence.
Example Output: a man watches two giraffes eating morf a box

Example Input: Sentence: 'several horses walking down the sand on the beach'. Reverse all words of length '3' in the given sentence.
Example Output:
several horses walking down eht sand on eht beach